Previous Year Questions: Carbon & its Compounds - 1

Ans: (c) C₇H₁₄

• Option (a), (b),and (d) all are alkanes
  C₄H₁₀ , C₆H₁₄, C₁₀H₂₂→ fits C_nH_2n+2 (n=4 → H=10)
• But C₇H₁₄ fits C_nH_2n, which is the general formula for alkenes, not alkanes.

Hence, C₇H₁₄ does not belong to the same homologous series as the others.

Ans: (d) It is an addition reaction which occurs in the presence of an acid catalyst.

Hydrogenation of vegetable oils is an addition reaction that occurs in the presence of nickel or palladium catalyst, not an acid catalyst. Hence, statement (d) is incorrect.

Ans: (d) Propyne

Propyne has one carbon-carbon single bond (C-C) and one carbon-carbon triple bond (C≡C).
Hence, it satisfies the given condition.

Ans: (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
Propanal (CH₃CH₂CHO) and propanone (CH₃COCH₃) have the same molecular formula (C₃H₆O) but differ in structure - one is an aldehyde and the other a ketone.
Hence, they are structural isomers, and the reason correctly explains the assertion.

Ans: (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).

Carbon and its compounds like coal, petroleum, and natural gas are major fuels because they release large amounts of heat and light on burning (combustion).
Thus, both statements are true, and the Reason correctly explains the Assertion.

Ans: (1) and (4)

• (1) Propanal (CH₃CH₂CHO) and (4) Butanal (CH₃CH₂CH₂CHO) both contain the -CHO functional group (aldehyde group).
• They differ by a -CH₂- unit, which is the defining feature of a homologous series.
• (2) is an ketone (-O group) and (3) is a carboxylic acid (-COOH group), so they belong to different series.

Hence, (1) and (4) are members of the same homologous series - the aldehyde series.

Ans: 
(i) 

A = Ethanol (CH₃CH₂OH) - a saturated two-carbon alcohol.

B = Ethanoic acid (CH₃COOH) - the organic acid formed on oxidation (molar mass 60 u).
Molar mass: 12×2 (C) +1×4 (H) +16×2 (O) =24+4+32=60 u
On heating ethanol with excess concentrated H₂SO₄ at 443 K, dehydration occurs forming ethene (C₂H₄)

Therefore, C = Ethene(CH₂=CH₂) - the unsaturated hydrocarbon formed on dehydration of ethanol.

(ii) Molecular Mass of  C₂H₄ → M = 2 × 12 + 4 × 1 = 28 u.
(iii) Ethanoic acid reacts with sodium carbonate to give sodium ethanoate, CO₂ and H₂O (effervescence of CO₂; CO₂ turns lime water milky). Balanced equation(iv) Electron Dot Structure of B (CH₃COOH):

Ans:
(i) Cl₂ Structure: 

Reaction:

Name of the reaction: Substitution reaction or photo-chemical reaction.

(iii) The two oxidising agents used are:

• Alkaline potassium permanganate (KMnO₄)
• Acidified potassium dichromate (K₂Cr₂O₇)

(iv) 

Ans:
(i) X: Ethanoic acid (CH₃COOH), commonly called acetic acid or vinegar.

• (Clues: 2 carbon atoms, turns blue litmus red, 5-8% aqueous solution used as preservative.)

Structure of CH₃COOH:  

(ii) pH Comparison: Ethanoic acid (weak acid, pH ~3-4) is less acidic than mineral acids (e.g., HCl, pH ~1).
(iii)  

• Reaction: Acetic acid + Alcohol → Ester + Water

• This reaction is called esterification.

Example with ethanol:

The product CH₃COOC₂H₅ (ethyl acetate) has a sweet smell, used in perfumes.

(iv)  Reaction with sodium carbonate 

• Reaction: Acetic acid + Sodium carbonate → Sodium acetate + Carbon dioxide + Water

• CO₂ is the colorless gas which turns lime water milky.

• Salt formed: Sodium acetate (CH₃COONa).

Ans: 
(a) Homologous Series for -CHO (Aldehydes)
Definition:
A homologous series is a family of compounds in which the same functional group is present and successive members differ by a -CH₂- unit. Members of a homologous series show similar chemical properties (because of the same functional group) and a gradation in physical properties with increasing molecular mass.

Aldehyde series (-CHO):
General formula: CₙH₂ₙO

Each member differs by a -CH₂- unit and has the same functional group (-CHO).

(b) Procedure:

1. Take two small test tubes. Put a little of the unknown compound in each (or use labelled samples: one known alcohol and one known carboxylic acid for demonstration).

2. Add a pinch (or a small spatula) of sodium carbonate (Na₂CO₃) to each test tube and observe.

Observation:

• The carboxylic acid reacts with sodium carbonate to produce effervescence (bubbling) due to the evolution of carbon dioxide (CO₂) gas.

• An alcohol does not produce CO₂ with sodium carbonate and therefore shows no effervescence.

Chemical Equation:
General reaction of a carboxylic acid (RCOOH) with sodium carbonate:

Example with ethanoic acid:

Conclusion:
Effervescence (CO₂ evolution) - the sample is a carboxylic acid. No effervescence - the sample is an alcohol.

Ans: 
Cyclic Hydrocarbons: Cyclohexane, Benzene.

(a) Cyclohexane Structure:

C₆H₁₂ (six-carbon ring, single bonds)

(b) Benzene Structure:

 C₆H₆ (ring with alternating double bonds)


(c) Micelle formation

When soap is added to water, the soap molecules arrange themselves into spherical structures called micelles.

Each soap molecule has two ends:

• A hydrophobic tail (long hydrocarbon chain) that repels water but attaches to oil or grease.

• A hydrophilic head (ionic end) that dissolves in water.

In water, the hydrophobic tails surround and trap the oily dirt in the centre, while the hydrophilic heads remain outward in contact with water. This forms an emulsion of oil in water known as a micelle, which can then be easily rinsed away, cleaning the dirt.

Ans: (A)

Alcohol: Ethanol (C₂H₅OH); Carboxylic Acid: Ethanoic acid (CH₃COOH).

Structures:

• Ethanol: 

• Ethanoic acid: 

Conversion of the alcohol into the carboxylic acid (oxidation) 

Ethanol is oxidised to ethanoic acid using an oxidising agent such as alkaline potassium permanganate (or acidified potassium dichromate) with heat:

Reaction between the alcohol and the acid in presence of an acid (esterification)
Ethanol reacts with ethanoic acid in the presence of an acid catalyst to give an ester (ethyl ethanoate) and water:(Ester formed: ethyl ethanoate, a sweet-smelling compound used in perfumes and flavoring.)

Ans:
(a) Element A has atomic number 16 → electron configuration 2, 8, 6 (valence = 6).
To attain the nearest noble-gas configuration (argon, with 8 in outer shell) it will gain 2 electrons to form the S²⁻ ion (or equivalently share electrons to complete its octet).
(b) Butene (C₄H₈): One C=C double bond and the rest single bonds).

• C-H single bonds: 8

• C-C single bonds: 2 (there are 3 C-C connections total, one of them is the double bond)
  So total single covalent bonds = 8 + 2 = 10.

• Double covalent bonds = 1 (one C=C).

(c) (A) NH₃ Formation:

Nitrogen (atomic no. 7) has 5 valence electrons. It needs 3 more electrons to complete its octet. Each hydrogen brings 1 electron; three H atoms share their electrons with N to form three N-H single covalent bonds. Nitrogen also retains one lone pair.

OR 
(c) (B) Carbon has 4 valence electrons; losing 4 electrons or gaining 4 electrons is energetically unfavourable. So carbon shares its four valence electrons with other atoms (including other carbon atoms) to attain a filled outer shell (noble-gas configuration). Sharing also allows strong C-C bonds (catenation), giving stable chains, rings and many compounds.

Ans: (c)

The correct answer is (c) because carbon compounds generally do not conduct electricity well (bad conductors), and they have weak forces of attraction between their molecules, which means the molecules can move around easily. This explains why carbon compounds often exist as gases or liquids rather than solids.

Ans: (A) (i) A homologous series is a group of carbon compounds where each member differs from the next by a CH₂ unit. They share the same functional group and exhibit similar chemical properties.
(ii) The melting and boiling points of C₄H₈ are higher than those of C₃H₆ or C₂H₄ because these points increase with molecular mass.
(iii) There is no gradation in the chemical properties of compounds in a homologous series because their properties are determined solely by their functional group, which remains constant.
(iv) (i) Aldehyde: Propanal

(ii) Ketone: Propanone

OR
(B) (i) The organic compound X with two carbon atoms and the suffix -ol is Ethanol.

(ii) When X is heated with excess concentrated sulphuric acid at 443 K, it undergoes dehydration to form ethene. The reaction can be represented as:

(iii)The hydrocarbon produced in the reaction is ethene.

Ans: (a)
In a homologous series of carbon compounds, like alkanes or alkynes, each member differs from the next by a specific group of atoms (-CH₂), which is explained in statement (A). As the size of the molecules increases (more carbon and hydrogen atoms), their melting and boiling points also generally increase, as stated in (B). Thus, both (A) and (B) are correct, making option (a) the right answer.

Ans: (a) (i) Carbon cannot form C⁴⁺ cations because removal of 4 electrons from a carbon atom would require a large amount of energy and it cannot form C^4- anion because it would be difficult for the nucleus with 6 protons to hold 10 electrons.
Thus it shares electrons to form covalent compounds.
(ii) A homologous series is a group of compounds that share the same functional group, with each member differing by a specific number of CH₂ units. For example, the molecular formulas of two consecutive members of the aldehyde series are:

• CH₃CHO (Ethanal)
• C₂H₅CHO (Butanal)

(iii)Structure of cyclohexane (C₆H₁₂)

OR
(b) (i)  A commercially important carbon compound with the functional group -OH is Ethanol with the molecular formula C₂H₅OH.
(ii)

NOTE: Name of the product for each reaction is given in bold letters under the reaction.

Ans: (b)
The correct structural formula for cyclohexane is shown in option (b). Cyclohexane, C₆H₁₂ , is a cyclic hydrocarbon with a six-membered ring structure, where each carbon atom is bonded to two other carbon atoms and two hydrogen atoms. This configuration ensures all carbon-carbon bonds are single, fitting the description and structure in option (b).

Ans: (b)

• The hydrocarbons C₄H₁₀ (butane), C₅H₁₂ (pentane), and C₂H₆ (ethane) are all alkanes, which are saturated hydrocarbons containing only single bonds.
• However, C₇H₁₄ is an alkene, which has at least one double bond.
• Therefore, option (b) is different from the others.

Ans: (a) The first two members of homologous series having functional group -Br. are CH₃Br, C₂H₅Br
(b) (i) Aldehyde (ii) Ketone
(c) When a 5% alkaline potassium permanganate solution is added drop by drop to warm ethanol in a test tube, the following is observed:

The purple colour of potassium permanganate fades, indicating a reaction.

The role of KMnO₄ in this reaction is as an oxidising agent.

OR
(c) When ethanol is heated at 443 K with excess concentrated H₂SO₄, the compound formed is Ethene. 

The role of concentrated H₂SO₄ is as a dehydrating agent. 
The chemical equation for this reaction is:

Ans: (b)

Six single bonds between Carbons and Hydrogens, three single bonds between six Carbons and Hydrogens ( alternatively) . Three double bonds present between carbons ( alternatively in hexagonal ring). So a total of nine single bonds, three double bonds are present in benzene ring.

Ans: 

(i) Low melting points and boiling points - Weak intermolecular forces of attraction.
(ii) Non-conductors of electricity - Bonding in these compounds does not give rise to any ions. / Covalent bonds or sharing of electrons do not form any charged particles.

Ans: (a) Hydrocarbons are compounds made up of carbon and hydrogen only.
(b) Two key properties that allow carbon to form a vast number of compounds are:

• Tetravalency: Carbon can form four covalent bonds.
• Catenation: Carbon atoms can bond with each other to form long chains.

(c) (i)

(c) (ii)  Structural isomers are compounds that have the same molecular formula but different structures. Two isomers of butane (C₄H₁₀) are:

Ans:

The products of the combustion reaction of a saturated hydrocarbon are:

• Carbon dioxide (CO₂)
• Water (H₂O)

Ans:

(i) Oxygen is added to ethanol to produce ethanoic acid. 

(ii) Alkaline potassium permanganate or Acidified potassium dichromate

(iii)

(iv) It is oxidation reaction while other is combustion reaction/ burning of ethanol is exothermic while other is endothermic.

Ans: As carbon has four valence electrons and it can neither loose nor gain four electrons thus, it attains noble gas configuration only by sharing of electrons. Thus, it forms covalent compounds. The existence of large number of compounds is due to some unique properties of carbon which are:
(i) Catenation: Carbon atoms possess an unique property to link together to form very long chains. This property is referred to as catenation.
A large number of carbon atoms can join together to form straight chains, branched chains and rings as shown below:

(ii) Tetravalency: Due to small size and presence of four valence electrons, a carbon atom can form multiple bonds with some other carbon atoms as well as with other atoms like oxygen, nitrogen etc., This increases the variety of compounds formed by it and hence the number of compounds is tremendously increased.
Due to small size, the nucleus of carbon atom can hold its shared pairs of electrons strongly. As a result, the bonds that carbon forms with most of the other elements such as hydrogen, oxygen, nitrogen, etc. are very strong there by making these compounds exceptionally stable.

Ans: (i) Structural isomers of butane are the following:


(iii) (a) Three homologue of alcohol are the following:CH₃OH, CH₃CH₂OH, CH₃CH₂CH₂OH
Third homologue of alcohol is CH₃CH₂CH₂OH
(b) Three homologue of aldehyde are the following:
HCHO, CH₃CHO, CH₃CH,CHO
Third homologue of aldehyde is CH₃CH₂CHO.
(iv) (a) Benzene (b) But-1-ene
(v) Z = 7,

Ans: (i) The process in which compounds of carbon react with oxygen to give carbon dioxide, water, heat and light, is known as combustion. Alkanes burn in air and release large amount of heat, therefore can be used as excellent fuels.

(ii) Oxidation is a process in which oxygen is added to a substance.

(iii) Hydrogenation means addition of hydrogen to an unsaturated compound.

(iv) When alcohol is added to carboxylic acid in the presence of acid catalyst then, a fruity smelling ester is formed. This process is called esterification.

(v) Esters react in the presence of an acid or a base to give the alcohol and carboxylic acid. This reaction is known as saponification because it is used in the preparation of soap.

Ans: (c)
Structure (I) is cyclohexane, a saturated cyclic hydrocarbon with single bonds between all the carbon atoms.
Structure (II) is benzene, an unsaturated cyclic hydrocarbon with alternating double bonds, giving it aromatic stability.
Structure (III) is cyclohexene, an unsaturated cyclic hydrocarbon with one double bond.
Thus, (I) is a saturated cyclic hydrocarbon, and (II) and (III) are unsaturated cyclic hydrocarbons, making (c) the correct answer.

Ans: (A) Ethanol (C₂H₅OH) belongs to alcohol's homologous series. 
A- Ethanol (C₂H₅OH) 
B- Ethene (C₂H₄) 
C- Ethane (C₂H₆) 
(B) Dehydration occurs when ethanol is heated with concentrated sulphuric acid at 443 K, resulting in the formation of ethene Concentrated sulphuric acid serves as a dehydrating agent in this reaction.
(C) Compound C is ethane. When it undergoes combustion, it forms CO₂ and water.
(D) Hydrogenation reactions are used in the production of saturated vegetable ghee from unsaturated vegetable oils. 
(E) Sodium ethoxide is formed when ethanol (C₂H₅OH) reacts with sodium (Na). The reaction is as follows:

Ans: Carbon forms compounds mainly by covalent bonding.Carbon primarily forms covalent compounds due to its unique electronic structure:

• Carbon has four electrons in its outer shell, making it challenging to gain or lose electrons to achieve a stable octet.
• To attain a stable configuration, carbon shares its valence electrons with other atoms, either with other carbon atoms or different elements.

This ability to share electrons leads to the formation of a vast number of compounds, including:

• Catenation: Carbon can bond with itself, creating long chains, branched structures, or rings.
• Strong bonds: The small size of carbon allows for strong interactions with shared electrons, resulting in stable compounds.

Overall, carbon's unique properties enable it to form a diverse range of stable covalent compounds.

Ans: (a) (i) Methane (CH₄)
(ii) Propane (CH₃CH₂CH₃) or C₃H₈
(b) Due to weak intermolecular forces of attraction, covalent compounds generally have low melting and boiling points.

Ans:  Covalent compounds have low melting and boiling points due to the following reasons:

• The forces of attraction between the molecules are very weak.
• A small amount of heat can easily break these molecular forces.
• This results in low melting and boiling points compared to other types of compounds.

Ans: Diamond is a well-known allotrope of carbon.

Ans: Carbon prefers to share its valence electrons with other atoms of carbon or with atoms of other elements rather than gaining or losing the valence electrons in order to attain noble gas configuration. Carbon has an atomic number of 6, meaning it has four electrons in its outer shell. Here are the reasons why it prefers sharing electrons:

• If carbon were to gain four electrons, it would form a C^4- anion. This would create strong repulsions among the eight electrons in the valence shell, making it hard for the nucleus to hold onto ten electrons.
• If it lost four electrons, it would create a C⁴⁺ cation. This process requires a significant amount of energy, as the nucleus would then only hold onto two electrons.

To overcome these challenges, carbon shares its valence electrons with other atoms. This sharing leads to the formation of a covalent bond, allowing both atoms to achieve a stable noble gas configuration.

Ans: (a) Formation of oxygen molecule:

(b) Formation of nitrogen molecule:

Ans: Carbon can form only covalent compounds because carbon can neither gain nor lose four electrons to acquire stable octet. The only way by which it can acquire the nearest noble gas configuration is by sharing its valence electrons with other C-atoms or atoms of other elements. Hence, carbon forms compounds mainly by covalent bonding.

Ans: (i)  Carbon compounds typically have low melting and boiling points because:

• They are held together by weak intermolecular forces.
• This weak attraction results in lower energy requirements to change states.

(ii) Carbon compounds do not contain ions and hence, are generally poor conductors of electricity.
(iii) Carbon can form only covalent compounds because carbon can neither gain nor lose four electrons to acquire stable octet. The only way by which it can acquire the nearest noble gas configuration is by sharing its valence electrons with other C-atoms or atoms of other elements.

Ans: 

(b) 

Ans: (a) (i) Methane (CH₄)
(ii) Propane (CH₃CH₂CH₃) or C₃H₈
(b) Due to weak intermolecular forces of attraction, covalent compounds generally have low melting and boiling points.

Ans: (a) C₃H₆(or C_nH_2n, n = 3) i.e, alkene series thus, has one double covalent bond.
(b) C₄H₆ (or C_nH_2n-2, n = 4) i.e., alkyne series.
The first member of alkyne series is ethyne (C₂H₂) HC ≡ CH.
(c) C₆H₁₂ can form ring structure of C-atoms.

(d) Alkane series: C_n H_2n+2
Only C₃H₈ is a member of alkane series CH₃ - CH₂ - CH₃

Ans: (a) General formula of alkyne C_nH_{2n - 2}
For C_xH₂, 2n - 2 = 2 ⇒ n = 2 ∴ x = 2.
For C₃H_y, n = 3, y = 2n - 2 = 2 x 3 - 2 = 4
Hence, x = 2, y = 4
(b) A is ethyne (C₂H₂) and B is propyne (C₃H₄).

Ans: A homologous series is the family of organic compounds having the same functional group, similar chemical properties but the successive (adjacent members of the series differ by a -CH₂ unit or 14 mass units.
(i) As the molecular mass increases in a homologous series, melting and boiling points also increases.
(ii) Chemical properties remains same for the members of homologous series because they all have same functional group.

Ans: 

These are called structural isomers as they have the same molecular formula i.e., C₄H₁₀ but different structures. As the molecular formula is C₄H₁₀, common name of this compound is butane. The alkyne of four carbon atoms is butyne. Its structure i is as follows:

The molecular formula of butyne is C₄H₆.

Ans: (i) Molecular formula of benzene is C₆H₆.

(ii) Number of single bonds = 9
Number of double bonds = 3
(iii) Alkynes are the unsaturated hydrocarbons that contain at least one triple bond between two carbon atoms (-C ≡ C-)

Ans: (a) Aldehyde (-CHO) group.
(b) C_nH_2nO
(c) Compound (i) is propanal, and compound (ii) is ethanal. They belong to the same homologous series where each successive compound differs from each other by a-CH₂ unit.
Other member of same homologous series:

Ans:  Covalent bonds are formed when two atoms share a pair of electrons. This sharing allows both atoms to achieve a stable electronic configuration, similar to that of noble gases.

• The shared electrons belong to the outermost shells of the atoms.
• Covalently bonded molecules have strong bonds within the molecule.
• However, the forces between these molecules (intermolecular forces) are generally weak.

Ans: Covalent compounds are generally poor conductors of electricity due to the following reasons:

• Covalent compounds do not contain ions.
• They consist of atoms that share electrons, rather than transferring them.
• This lack of charged particles means they cannot conduct electricity effectively.

Ans: A cyclic unsaturated carbon compound is a compound that contains a carbon ring with one or more double or triple bonds between the carbon atoms. An example of a cyclic unsaturated carbon compound is benzene, which has a ring of six carbon atoms with alternating double bonds.

Ans:  Carbon is unique among group 14 elements due to its ability to form a vast number of compounds, estimated at around three million. This is primarily because of two key properties:

• Catenation: Carbon can bond with itself, creating long chains, branched structures, or rings. This allows for the formation of large molecules.
• Bond Strength: Carbon forms strong bonds with other elements, including single, double, and triple bonds. This stability is due to its small size, which allows the nucleus to hold onto shared electrons effectively.

In contrast, other elements in this group, like silicon, can form fewer and less stable compounds. Their bond energies decrease as you move down the group, leading to limited catenation.

Ans: (i) 5% solution of KMnO₄ is prepared by adding 5 g of KMnO₄ in 95 g of water.
(ii) Here alkaline KMnO₄ acts as an oxidising agent. It oxidises ethanol to ethanoic acid by donating nascent oxygen. If excess of KMnO₄ is added the purple colour will persist indicating no more alcohol is left and reaction stops.
(iii)

Ans: (a) Isomers are those molecules which have the same molecular formula but different structural formulae i.e., show different properties and the phenomenon is called isomerism. The structures of possible isomers of butane (C₄H₁₀) are:
(b) The compound 'X' is likely an unsaturated compound (such as an alkene or alkyne) that burns in air, producing a yellow, sooty flame with significant smoke.
(c) Alkaline KMnO₄ acts as an oxidising agent which oxidise alcohol (-OH) to corresponding carboxylic acid (-COOH).

Ans: (a) A homologous series is a group of organic compounds that share the same functional group and have similar chemical properties. Each successive member of the series differs by a -CH₂- unit or 14 mass units.

• The alkane series, for example, has the general formula C_nH_2n+2.
• The first member is methane (CH₄).
• The second member is ethane (C₂H₆).
• The third member is propane (C₃H₈).

(b) (i) Carboxylic acids react with alcohols in the presence of a little concentrated sulphuric acid to form pleasant smelling esters. This reaction is called esterification reaction.

(ii) Those reactions in which atoms or group of atoms are simply added to a double or triple bond without the elimination of any atom or molecule, are known as addition reactions.

Ans: (a) (i) When ethanol is heated with cone. H₂SO₄ at 443 K, ethene is obtained due to dehydration of ethanol.

(ii) When 5 % alkaline KMn04 solution is added drop by drop to warm ethanol then it gets oxidised to ethanoic acid.

(b) Addition reactions: Those reactions in which atoms or group of atoms are simply added to a double or triple bond without the elimination of any atom or molecule, are known as addition reactions.
Substitution reactions: The reactions which involve the displacement or substitution of an atom or a group of atoms in an organic compound by another atom or group of atoms, are known as substitution reactions. Saturated hydrocarbons are fairly unreactive and inert in the presence of most of the reagents. However, in presence of sunlight, hydrocarbons undergo rapid substitution reactions. e.g.,

Ans: (a) As the molecular mass of Y is 30 g mol^-1, it is ethane (C₂H₆ = 12 x 2 + 6 x 1 = 30).
'X' is ethene (CH₂ = CH₂) which decolourises Br₂  water and burns with a smoky flame.



(c)  No, you cannot determine if water is hard using a detergent. This is because detergents function effectively in both hard and soft water. The calcium and magnesium salts of detergents are soluble, allowing them to work well even in hard water.

Ans: (b)
Assertion (A): Esterification is a process in which a sweet-smelling substance is produced. This is true. Esterification is a chemical reaction between an acid (usually a carboxylic acid) and an alcohol, resulting in the formation of an ester, which typically has a fruity or sweet smell.
Reason (R): When esters react with sodium hydroxide, an alcohol and sodium salt of carboxylic acid are obtained. This is also true. This reaction is known as saponification, where an ester reacts with a strong base to produce an alcohol and the salt of a carboxylic acid.
Since both statements are true, but the reason does not explain the assertion (as esterification and saponification are different processes), the correct answer is (b) Both (A) and (R) are true, and (R) is not the correct explanation of (A).

Ans: (d)
Assertion (A): Carbon has a strong tendency to either lose or gain electrons to attain noble gas configuration. This is false. Carbon does not lose or gain electrons easily because that would require a lot of energy. Instead, it tends to share electrons.
Reason (R): Carbon has four electrons in its outermost shell and has the tendency to share electrons with carbon or other elements. This is true. Carbon typically forms covalent bonds by sharing electrons to achieve a stable electron configuration.
Since the assertion is false but the reason is true, the correct answer is (d) (A) is false but (R) is true.

Ans: Oils that are best for cooking are those rich in unsaturated fatty acids. These oils are beneficial for health, while animal fats typically contain saturated fats, which can be harmful.

• Choose oils like olive oil, canola oil, and sunflower oil.
• Avoid animal fats such as butter and lard.
• Unsaturated fats can help reduce cholesterol levels.

Ans: A homologous series is defined as a group of compounds having the same functional group, similar chemical properties in which the successive members differ by a -CH₂ group or 14 mass unit.
For example, in alkane homologous series, the general formula is C_nH_2n+2 i.e.; first three members are CH₄. C₂H₆ and C₃H₈ where two successive members differ by -CH₂ group.
Characteristics of homologous series: 

• All compounds in the series can be represented by a general formula, e.g., for alcohol it is C_nH_2n+1OH, for alkane C_nH_2n+2, for alkene C_nH_2n and for alkynes C_nH_2n-2, where, n = 1, 2, 3..... 
• All compounds in the series have similar chemical properties. 
• All members of the series, show a gradual change in their physical properties.
• Physical properties generally increase as the molecular mass increases.

Ans: When a 5% alkaline potassium permanganate solution is added drop by drop to warm propanol, a chemical reaction occurs:

• The propanol is oxidised to propanoic acid.
• In this process, the alkaline potassium permanganate acts as the oxidising agent.

The chemical equation for this reaction is:

Ans: (A) S is a saturated hydrocarbon.
(B) Q is an organic acid.
Structural formula:

Ans: As X reacts with conc. H₂SO₄ to give an alkene so it should be an alcohol as cone. H₂SO₄ acts as a dehydrating agent. The reaction of X with Na also confirms that it is an alcohol because alcohols react with Na metal to evolve colourless hydrogen gas.

Here, cone H₂SO₄ acts as a dehydrating agent i.e., helps in the removal of water.

Ans: (a)  Most carbon compounds are poor conductors of electricity because:

• Carbon forms covalent bonds with other elements.
• There are no mobile electrons in these compounds.
• Carbon compounds do not dissociate into ions.

(b) Structure: 

Name: Cyclopentane
Number of single bonds: 15
Structure: C₅H₁₀

Ans: (a)
 
(b) Reaction of Ethanol with Sodium Metal:

• When ethanol reacts with sodium metal, hydrogen gas is released.
• Ethanol behaves like an acid in this reaction.

(c) structure of cyclohexane is below-

(d) Name of the compound is Ethanal and it is an Acetaldehyde 

Ans: When ethanol reacts with sodium metal, it forms sodium ethoxide (C₂H₅O^- Na⁺) and hydrogen gas is released. The reaction is as follows:
So, the gas is hydrogen that is evolved during the reaction.

Ans: The molecular formula of first two members of homologous series having - Cl functional group are CH₃CI and CH₃CH₂CI.

Ans: The molecular formula of first two members of homologous series having - OH functional group are CH₃OH and CH₃CH₂OH.

Ans: Homologous series of alkenes have general formula, C_nH_2n whose first member is ethene.
2^nd member of homologous series of alkenes is C₃H₆ i.e., propene.
3^rd member of homologous series of alkenes is C₄H₈ i.e., butene.

Ans: Methane, CH₄ is an alkane. Alkanes have general formula, C_nH_2n+2.
2^nd member of homologous series of alkanes is C₂H₆ i.e., ethane.
3^rd member of homologous series of alkanes is C₃H₈ i.e., propane.

Ans: All unsaturated hydrocarbons (containing double or triple bonds) have tendency to get converted to saturated hydrocarbons (single bonds) by adding small molecules such as hydrogen (H₂), halogens (X₂), etc. Such reactions are called addition reactions. Compound with the molecular formula C₄H₈ belongs to alkene series (C_nH_2n). Hence, it will undergo addition reaction.

Ans: The molecules of soap are sodium or potassium salts of long-chain carboxylic acids. Detergents are generally ammonium or sulphonate salts of long chain carboxylic acids.
Difference between Soap and Detergent
Soaps:
(i) Soaps are sodium salts of long chain carboxylic acids.
(ii) The ionic group in soap is -COO^-Na⁺.
(iii) Soaps are not useful when water is hard.
Detergents
(i) Detergents are the odium salt of long chain benzene sulphonic acids.
(ii) The ionic groups in detergents is SO₃^-Na⁺ or SO₄^-Na⁺.
(iii) Detergent can be used for washing purpose even when water is hard
Cleansing action of soap can be described as follows:
The soap molecule is generally represented as RCOONa. In solution, it ionises to form RCOO^- and Na⁺. Each soap molecule has a polar head group (carboxylate ion, COO^- group) and a long nonpolar hydrocarbon tail (R group from long chain fatty acid). The polar head attracts the polar water molecule and is called hydrophilic end and the nonpolar tail attracts the water-insoluble oily or greasy dirt particles.

Ans: Compounds consisting of carbon and hydrogen are known as hydrocarbons.
(a) Saturated hydrocarbons: Alkanes (C_nH_2n+2) are the compounds of carbon that have a single bond.

(b) Unsaturated hydrocarbons: The compounds of carbon having double bonds are alkene (C_nH_2n) and having triple bonds are alkyne (C_nH_2n-2). The reaction which converts unsaturated hydrocarbons to saturated hydrocarbons i.e. alkenes to alkane is known as hydrogenation reaction. It is used to obtain ghee from oil.

Ans: (a)
Soap forms lather easily in soft water, while hard water (which contains calcium and magnesium ions) reacts with soap to form scum, preventing the formation of lather.
In this case:
(i) Test tube P contains Na₂SO₄ (sodium sulfate), and Test tube Q contains K₂SO₄ (potassium sulfate). Both sodium and potassium salts do not contribute to water hardness, so they will allow soap to form lather.
(ii) Test tube R contains CaSO₄ (calcium sulfate), and Test tube S contains MgSO₄ (magnesium sulfate). Both calcium and magnesium contribute to water hardness, which prevents lather formation.
Therefore, a good amount of lather will be obtained in test tubes P and Q.

Ans: (d)
In this scenario:

• Sample C is kept at 95 ºC, which is close to boiling temperature. At this high temperature, the temporary hardness will be significantly reduced due to the decomposition of bicarbonates, allowing more lather to form when soap is added.
• Samples A (at room temperature) and B (at 50 ºC) will still retain more temporary hardness than sample C, and therefore will produce less lather.

Thus, sample C will give the maximum amount of lather, making the correct answer (d) C only.

Ans: A saturated hydrocarbon is a type of hydrocarbon where the carbon atoms are connected by only single covalent bonds. This means that each carbon atom is bonded to as many hydrogen atoms as possible.The formula for one example of a saturated hydrocarbon is CH₄, which is known as methane.

Ans: (c)
When ethanol (C₂H₅OH) reacts with sodium (Na), it forms sodium ethoxide (C₂H₅ONa) and hydrogen gas (H₂) as products. The reaction is as follows:In this reaction, sodium displaces hydrogen from ethanol, resulting in the formation of sodium ethoxide and the release of hydrogen gas.
Thus, the correct answer is (c) sodium ethoxide and hydrogen.

Ans. (i) C₂H₄ belongs to alkene series having general formula, C_nH_2n.
Thus, next homologue will be C₃H_2x3 = C₃H₆
(ii) C₄H₆ belongs to alkyne series having general formula, C_nH_2n-2.
Thus, next homologue will be C₅H_2x5-2 = C₅H₈ 

Ans: (a) CH₃ - CH₂ - OH: Ethanol (Alcohol)
(b) 

Ans: Saturated hydrocarbons (alkanes) follow the general formula C_nH_2n+2. From the given compounds, the following satisfy this formula:

• C₄H₁₀
• C₆H₁₄

Ans: An alcohol with three carbon atoms is called propanol. Its structure can be represented as follows:

• Carbon chain: C-C-C
• Hydroxyl group: -OH attached to one of the carbons

In summary, propanol consists of:

• Three carbon atoms
• One hydroxyl group

Ans: An alcohol with four carbon atoms is butanol and its structure is:

Ans: An aldehyde with four carbon atoms is butanal and its structure is:

Ans: Carbon exhibits the property of catenation to the maximum extent due to several key factors:

• Carbon can form strong bonds with other carbon atoms, creating large and complex molecules.
• This ability allows for various structures, including long chains, branched chains, and rings.
• Carbon's small size contributes to the strength of the carbon-carbon bonds, making them stable.
• With a valency of four, carbon can bond with up to four other atoms, enhancing its versatility.

Other elements, like silicon, show limited catenation, forming fewer and more reactive compounds.

Ans: The general formula of the alkane series is C_nH_2n+2. For fourth member of alkane series, n = 4
∴ C₄H_{2 x 4 + 2} = C₄ H₁₀ i.e., butane.

Ans:  A homologous series is a group of organic compounds that share the same functional group and exhibit similar chemical properties. The key characteristics include:

• Each member differs from the next by a -CH₂- unit.
• They have a consistent pattern in their physical properties, such as boiling points and solubility.
• The chemical properties remain similar due to the presence of the same functional group.

For example, compounds like alcohols and alkenes form homologous series where each successive compound has one more carbon atom than the previous one.

Ans: (i) When ethanol reacts with ethanoic acid in the presence of concentrated H₂SO₄, the product formed is ethyl ethanoate, which belongs to the class of ester compounds known for their fruity smell.

 (ii) The role of concentrated H₂SO₄ in this reaction is two fold:

• It acts as a dehydrating agent, helping to remove water.
• It serves as a catalyst to speed up the reaction.

Ans: Ethanoic acid reacts with sodium as well as sodium hydroxide to form sodium ethanoate.

Ans: Ethanoic acid reacts with Na₂CO₃ to form sodium ethanoate and CO₂ gas is liberated.

With sodium hydrogen carbonate it forms sodium ethanoate.

With NaOH It forms sodium ethanoate.

Ans: Tests for distinguishing between an alcohol and a carboxylic acid are:
(i) Litmus test: When we place a drop of carboxylic acid on blue litmus paper it turns red while alcohol will not change the colour of blue litmus paper.
(ii) Sodium hydrogen carbonate test/sodium carbonate
test: If a pinch of NaHCO₃ or Na₂CO₃ is added to two test tubes containing alcohol and carboxylic acid respectively, then test tube containing carboxylic acid will show the evolution of colourless gas with brisk effervescence while test tube containing alcohol does not show any reaction.

Ans: A micelle is a tiny cluster of molecules with non-polar groups inside and hydrophilic groups outside. When soap is added to water:

• The hydrophobic tails of soap molecules avoid water, forming a cluster.
• The hydrophilic heads remain in contact with water, stabilising the structure.

If ethanol is used instead of water, micelles will not form because ethanol lacks the necessary polar characteristics.The formation of micelles helps clean oily spots on clothes by:

• Trapping oily dirt in the centre of the micelle.
• Allowing the dirt to be easily rinsed away due to the colloidal nature of micelles.

Thus, soap effectively removes grease and dirt from fabrics.

Ans: (c)
The molecular formula C₄H₁₀ represents butane and its isomer isobutane (also called 2-methylpropane).
Structures (I) and (II)in the image represent these two structural isomers of C₄H₁₀:
(I) shows a straight chain structure (n-butane).
(II) shows a branched structure (isobutane or 2-methylpropane).
Thus, the correct answer is (c) (I) and (II).

Ans: Catenation is the ability of an atom to bond with other atoms of the same element. This property is notably exhibited by both carbon and silicon, but carbon demonstrates it to a far greater extent.

• Carbon can form long chains, branched structures, or rings due to its strong carbon-carbon bonds.
• Carbon has a valency of four, allowing it to bond with up to four other atoms, including other carbon atoms.
• This results in a vast number of stable compounds, as the bonds formed are strong and do not easily break.
• In contrast, silicon can form chains of only seven or eight atoms with hydrogen, but these compounds are highly reactive.

Overall, the unique ability of carbon to catenate leads to an extensive variety of compounds, making it essential for life and numerous applications.

Ans: Homologous series of alkenes have general formula, C_nH_2n whose first member is ethene.
2nd member of homologous series of alkenes is C₃H₆ i.e., propene.

Ans: Alkanes have general formula, C_nH_{2n + 2}.
2^nd member of homologous series of alkanes is C₂H₆ i.e., ethane.

Ans: General formula, C_nH_2n-2 belongs to alkyne series. The second member of this series is propyne i.e., (C₃H₄) or CH₃-C≡CH.

Ans: The structural formula of ethane (C₂H₆) is
There are total 7 covalent bonds. Six C - H covalent bonds and one C - C covalent bond.

Ans: Butane (C₄H₁₀) has the following structural formula as:

 Butane (C₄H₁₀) contains a total of 13 covalent bonds. This includes:

• 10 C - H bonds
• 3 C - C bonds

Ans: The process of adding hydrogen to an unsaturated compound is called hydrogenation. For example, the hydrogenation of ethene leads to the formation of ethane.

Conditions for Hydrogenation
(i) Presence of an unsaturated compound (i.e. an unsaturated hydrocarbon)
(ii) Presence of a catalyst such as finely divided palladium or nickel
In case of the hydrogenation of vegetable oils, liquid unsaturated fatty acids are converted into solid saturated fatty acids.