MPTET Varg 1 Chemistry Mock Test - 1 - MPTET MCQ

''Learning and knowledge are the greatest assets of a man'

• उक्त वाक्य का सही हिंदी रूपांतरण होगा -."सीख और ज्ञान मनुष्य की सबसे बड़ी सम्पत्ति है।"
• अन्य विकल्प अनुचित है।

स्पष्टीकरण
वाक्य के महत्वपूर्ण शब्दों का हिंदी अनुवाद -

• Learning - सीखना
• knowledge - ज्ञान
• greatest - महानतम।
• assets - सम्पति

अन्यसंबंधित बिंदु
assets शब्द से बने अन्य वाक्य -

• The river is a real asset. - नदी एक वास्तविक संपत्ति है।

सही उत्तर इसका दायित्व अब मेरे कन्धों पर है| है|
प्रमुख बिंदु

• समझदार का अर्थ है intelligent जिसका प्रयोग यहाँ नहीं किया गया है अतः यह विकल्प सही नहीं है,
• अगले विकल्प में क्षमता शब्द का प्रयोग है जिसका अर्थ है capability और इस शब्द का प्रयोग यहाँ नहीं किया गया है अतः यह विकल्प भी उपयुक्त नहीं है,
• दायित्व का अर्थ है responsibility और अंतिम विकल्प में given का अर्थ नहीं दिया गया है|
• अतः सही अनुवाद है इसका दायित्व अब मेरे कन्धों पर है|

The correct answer is "weak"
Explanation

• Weary refers to being exhausted, tired, or fatigued, both physically or mentally. It can also refer to being discouraged, skeptical or skeptical about something. 
  • Example: "The marathon runner felt weary after running for 26 miles."

Let's see the meanings of the given words

• Careless refers to being negligent or not paying attention to details, which often results in mistakes or accidents. It also means someone who is not taking responsibility or not being cautious. 
  • Example: The careless driver caused an accident by running a red light."
• Shivering refers to a physical reaction characterized by rapid, small, involuntary muscle contractions that results in a trembling of the body, usually as a response to cold or fear. 
  • Example: "The shivering child was wrapped in a blanket to keep warm."
• Troubled refers to being in a state of distress, anxiety, or difficulty. It can also refer to a person who is experiencing personal or emotional problems.
  • Example: "The troubled economy was causing widespread unemployment."
• Weak refers to something that is lacking in strength, power, or force, or something that is not substantial or effective. It can also refer to a person who is not physically or mentally strong.
  • Example: "The weak connection caused the internet to drop frequently."

According to the meanings of the given words, the correct answer is Option 4, i.e., weak.

The correct answer is - "Kind"
Explanation

• Benevolent means kind, friendly and helpful to others 
  • Eg. He was a benevolent old man, he wouldn't hurt a fly.
• Kind means caring about others; friendly and generous
  • Eg. Everyone’s been so kind to us since we came here!
• From the given options, Kind is the appropriate SYNONYM of the Benevolent.
• Thus, Option 3 is the correct answer.

Other Related Points

• Beneficial means having a good or useful effect
• Helpful means giving help
• Supportive means giving help or support to somebody in a difficult situation

Teaching-learning aids are the tools used by teachers to help learners to learn concepts with ease and efficiency. Teaching-learning materials provide a range of learning experiences to learners from direct to indirect.

ExplanationTeaching learning aids can broadly be classified into three categories.

• Audio aids
• Visual aids
• Audio-Visual aids

The following principles make the use of Teaching Aids effective:

• Principle of Selection: as per the teaching objectives and unique characteristics of the learners.
• Principle of Preparation: All teachers should be able to prepare some of their own Teaching Aids.
• Principle of Physical Control: Proper preparation of the aids safely.
• Principle of Proper Presentation: Proper presentation of the teaching Aids is very necessary.
• Principle of Response: help the students to respond actively to the audio-visual so that they derive the maximum benefit in learning.
• Principle of Evaluation: There should be continuous evaluation of both the use of the aids and the realization of the desired objectives.

Hence, we can conclude that the principle of Observation is not used for preparing the audio-visual aids.

Important Points

• The principle of observation is the art and skill of passing knowledge or ideas by viewing the actions of a model from which one imitates. It is also known as the social learning theory.
• Visual teaching aids-Through this teaching aid we teach the students to show the poster and chart.
• Audio teaching aid- By this teaching aid, we teach the student by speaking something.
• Audio-visual teaching aid- Through this teaching aid we teach the students to show something and to speak both.

Teaching and learning are two interrelated concepts in the education system. Learning as a process is the formation of a bond between stimulus and response and is reinforced by the emitted response. Teaching is an activity that results in a change in the behavior or response of the learner.

Explanation

There are many factors that affect learning. Students' related factors are the elements of students' personalities that limit or enhance the ways they learn and think.

The factors affecting the teaching-learning process related to students are:

• Age and maturation
• Physical and mental health
• Emotional conditions
• Interest and motivation
• Readiness and willingness, etc.

Hence, we can conclude that all of the above is correct in the context of the question.

Problem-solving skills are skills that enable people to handle unexpected situations or difficult challenges at work. Problem-solving is an essential skill in the workplace and personal situations. Problem-solving and decision making are closely related skills, and making a decision, solving may sound obvious but often requires more thought and analysis.

Explanation

Problem-solving abilities are skills that allow individuals to efficiently and effectively find solutions to issues. These skills include the following:

Important Points

• Problem-solving is the ability to use appropriate methods to tackle unexpected challenges in an organized manner.
• Problem-solving is a mental process and is related to the analytical power of the brain that concludes the part of the larger problem process that includes problem finding and problem shaping.
• It is based on the conviction that an analytic mind and perseverance can help in overcoming problems. Therefore, it reposes faith in the ability of distant learners to analyze the problematic situation and identify the resources at their disposal with which they can overcome the problem.
• Analytic skills allow us to evaluate problems, both simple and complex.
• Effective problem solving requires a controlled mixture of analytical and creative thinking.
• The act of defining a problem, determining the cause of the problem, identifying and selecting alternatives for a solution, and implementing a solution.
• Problem-solving is all about using logic as well as imagination to make sense of a situation and come up with an intelligent solution.

Hence, we can conclude that problem-solving skill is related to analytical power of the brain.

Basic education was introduced in India by Gandhiji.

Explanation

• Mahatma Gandhi was the founding father of Basic Education.
• The founding father of Basic education is the father of the nation, Mahatma Gandhi.
• Mahatma Gandhi introduced Basis education in his ashram in the year 1946.
• Basic education is a principle that states that knowledge and work aren't separate.

Other Related PointsMahatma Gandhi promoted an academic curriculum with the same name based on this pedagogical principle. It can be translated with the phrase 'Basic Education for all. The term ‘Basic’ is critical in Basic Education. Basic comes from the term “Base”. which means bottom or foundation. so, in the literary sense, Basic Education is the foundation of education or education at the primary level on which the edifice of the structure of higher education can be built.

Basic Education theme pattern:

• Pre-basic (up to six years )
• Basic (from seven to fourteen years)
• Post-Basic (from fifteen to 18)
• University education
• Social and adult education

Concept:
Isobars:

• Isobars are atoms which are having the same mass number but their atomic number is different. or we can say Isobars have different atomic numbers, i.e., the number of protons but the same mass number, i.e., the sum of the number of protons and neutrons.

Explanation:
Isotopes:

• Elements having the same atomic number but a different mass number are called isotopes or Elements with the same number of electrons but a different number of neutrons are called isotopes.

Isotones:

• Elements having the same number of neutrons but different numbers of electrons are called isotones.

Isobars:

• If the Sum of the number of protons and neutrons (is equal to the mass number of an atom) is the same but the number of protons is different the atoms are called isobars.
• Isotopes are the chemical properties of an atom that are controlled by the number of electrons, which are determined by the number of protons in the nucleus.
• The number of neutrons present in the nucleus has very little effect on the chemical properties of an element.
• Therefore, all the isotopes of a given element show the same chemical behavior.

Conclusion:
Two atoms are said to be isobars if the sum of the number of protons and neutrons is the same but the number of protons is different.
Other Related Points
Atomic number (Z) = number of protons in the nucleus of an atom = number of electrons in a neutral atom.

→ Hinsberg test is employed to separate primary, secondary and tertiary amines from a mixture.
→ In this test, the mixture of amines is treated with benzene sulphonyl chloride C₆H₅SO₂Cl (Hinsberg's reagent) followed by treatment with aqueous KOH (5%) solution and then shaken with ether in a separatory funnel.
→ Hofmann's method to separate amines in a mixture uses the reagent diethyl oxalate. The mixture of the three amines is heated with diethyl oxalate. Primary amine forms solid oxamide, the secondary amine forms a liquid oxamic ester and the tertiary amine does not react at all.
→ The Mixture of 1°, 2°, and 3° amines can be separated by distillation as they differ in boiling points.

Concept:
Boyle’s law:
The volume of a given gas is inversely proportional to the pressure of the gas when the temperature is kept constant.
Mathematical Expression;
So, PV = Constant
Explanation:
According to Boyle’s law, at a constant temperature, PV = Constant.
So, P₁V₁ = P₂V₂ = P₃V₃ = P₄V₄
From the graph;

Slope values decrease as we go from pressure line P₁ to P₂.
Pressure is inversely proportional to volume.
Graph indicates that, P₁ < P₂ < P₃ < P₄
From P₁ to P₄ increase, hence volume V₁ to V₄ must be decreased.
V₁ > V₂ > V₃ > V₄
Conclusion:
Correct option is (3) P₁ < P₂ < P₃ < P₄.

Concept:

• The first step is to count the longest chain of carbons. The longest chain has to be continuous.
• In the second step, we have to count the number of carbons present in the chain beginning with the side which is close to the branch. We call the longest chain present in branched alkane as the parent chain.
• In the third step, we have to count the number of carbons present in each branch. The carbons present in branches are called alkyl groups and they contain one carbon less than the alkane group. For example, if there is one carbon present, we call the group a methyl group, if it’s two carbons, then it is ethyl, and so on.
• We have to attach the number of carbon from each substituent branch to the front of the alkyl group name. For example, if a group containing two carbons is bonded to a third carbon present in the chain, then we call the group as 3-ethyl.
• In the fifth step, we have to check for repeated alkyl groups. If we notice multiple groups present with the same number of carbons branched off the parent chain, we should not repeat the name. In such instances, we have to use prefixes such as di-, tri-, and tetra-.
• In the sixth step, we have to place the names of the substituent groups before the name of the parent chain in alphabetical order. We need not alphabetize the prefixes such as di-, tri-, and tetra-.

Explanation:

• Nomenclature means naming of organic compounds.
• It is written as: Secondary prefix + primary prefix + word root + primary suffix + secondary suffix.
• The substituent of the base compound is considered to be number 1, and then the direction of numbering is chosen such that the next substituent group is getting the lowest number.
• The substituents appear in the name, arranged in alphabetical order.
• If different substituents are attached to the benzene, then the numbering of the chain can be done in such a way that gives the lowest number to the substituents.
• The substituents are written in alphabetical order.
  
• So, the name of the compound can be written as 1−Chloro-4−methyl-2−nitrobenzene.

Conclusion:
Therefore, the name of the compound can be written as 1−Chloro-4−methyl-2−nitrobenzene.

Saytzeff's rule: According to this rule, the major product is that alkene which has a greater number of an alkyl group(s) attached to the doubly bonded carbon atoms.
The major product formed in the dehydrohalogenation reaction of 2-bromopentane is pent-2-ene because
According to Saytzeff's rule, in dehydrohalogenation reactions, the preferred product is that alkene which has a greater number of alkyl group(s) attached to the doubly bonded carbon atoms

Concept:

According to Gibb's Phase rule,

Where,

F is the the number of degrees of freedom, C is the number of chemically independent constituents of the system, and P is the number of phases.

Explanation:

We know that,

Given,

For one component system,

Now we get,

For P to be maximum, F should be equal to zero.

Hence,

Conclusion: -

The maximum number of phases that can be simultaneously in equilibrium for a one component system is 3. So the option 3 is correct.

The correct answer is ​Sodium benzoate.

Explanation

• Sodium benzoate is a preservative that is most widely used in acidic foods such as salad dressings, carbonated drinks, jams and fruit juices, pickles, condiments, and yoghurt toppings.
• Food preservation is a method to protect food from unwanted microbial growth and is done to preserve food for a longer time.
• Sodium benzoate is a widely used preservative found in many foods and soft drinks to prolong shelf life.
• It is an odourless, crystalline powder made by combining benzoic acid and sodium hydroxide.
• Benzoic acid is a good preservative on its own, and combining it with sodium hydroxide helps it dissolve in products.
• Sodium benzoate does not occur naturally, but benzoic acid is found in many plants, including cinnamon, cloves, tomatoes, berries, plums, apples, and cranberries.

Other Related Points

Concept:

• The oxidizing agent contains the species being reduced and therefore decreasing in oxidation number (it is the whole molecule/ion containing that species).
• The oxidizing agent takes electrons from the species being oxidized.
• The reducing agent contains the species being oxidized and therefore increasing in oxidation number (it is the whole molecule/ion containing that species).
• The reducing agent donates electrons to the species being reduced.

Explanation:

• In an acidic medium, permanganate ion (MnO₄^-) is reduced to manganese (II) ion.
• Manganese atoms are balanced on the reactant and product side.
• Oxygen atoms are balanced by adding water molecules to the appropriate side and hydrogen is balanced using protons as the reaction is carried out in the acidic medium.
• In order to balance the equation, the electrons are added to the appropriate side in order to balance the charge.
• From the stoichiometry of the reaction, it can be seen that one mole of MnO₄^- accepts 5 electrons in a redox process.

Conclusion:
Thus, in an acidic medium, one mole of , accepts 5 moles of electrons in a redox process.

Molecularity-

• The number of reacting particles (molecules, atoms, or ions) that collide simultaneously in a rate-determining step to form a product is called the molecularity of a reaction.
• In general, the molecularity of simple reactions is equal to the sum of the number of molecules of reactants involved in the balanced stoichiometric equation.
• The Molecularity of a reaction is always in the whole number.
• It is never fractional.
• Molecularity is a theoretical concept.
• Molecularity cannot be greater than three because more than three molecules may not mutually collide with each other.

Correct answer: 4)

Concept:

• A mole is formally defined as the amount of substance containing the same number of discrete entities (such as atoms, molecules, and ions) as the number of atoms in a sample of pure ¹²C weighing exactly 12 g.
• One mole of a substance is equal to 6.022 × 10²³ units of that substance (such as atoms, molecules, or ions).
• The number 6.022 × 10²³ is known as Avogadro's number or Avogadro's constant.

Explanation:

Molar mas of BaSO₄ = 233.3 g/mol

Moles of BaSO₄ =

=0.0079 moles

BaCl₂.xH₂O + H₂SO₄ → BaSO₄ + xH₂O +zHCl

Molar mass of BaCl₂ =208.3 g/mol

The number of moles of BaCl₂= 0.0079 moles

Gram of BaCl₂ = mass x moles of BaCl₂

= 208.3 g/mol x 0.0079 moles

= 1.645 g

Mass of water = Gram of BaCl₂. XH₂O - Gram of BaCl₂

= 1.936- 1.645

=0.291 g

No. of moles of water =

=

=0.016 moles

The ratio of number of moles of water to BaCl₂ (x) =

x =2.02

Conclusion:

Thus, the value of X is 2.

Haloalkanes-

• Haloalkanes are generally colorless and odorless compounds.
• Boiling point –
  • The boiling point of haloalkanes is higher than alkanes if the number of carbon atoms is the same in both.
  • The boiling point of haloalkanes al so increases with the increasing number of halogens in haloalkanes. It means 1-Bromo-2-chloroethane will have a higher boiling point than chloroethane.
  • Boiling points of haloalkanes scale with the atomic weight of halides. Although fluoroalkanes are exceptions. They show a lower boiling point than their analogous alkanes. It is due to the lower polarizability of fluorine. The boiling point of 2- methylpropane is -11.7℃ while 2- fluoropropane is -10℃.
  • As the branching increases, boiling points of isomeric haloalkanes decrease. For example, the boiling point of 1-bromobutane is 375K while 2-bromopropane is 346K
  • The boiling point increases with an increase in the size of the hydrocarbon part for the same haloalkanes.

Given data and Analysis-
All the given haloalkanes and haloarenes contain the same halogen atom i.e., bromine but the number of carbon atoms in the hydrocarbon part of the molecule is increasing from ethane to benzene.
So, the boiling point is minimum for 1-bromoethane and maximum for 1-bromobenzene.
So the correct order will be 1-bromoethane < 1-bromopropane < 1-bromobutane < Bromobenzene.

Concept:
Ambidentate nucleophile -
The nucleophile that can attack through two different sites is called an ambident nucleophile.
For ex -CN^- is an ambient nucleophile as it can attack through either C or N and give alkyl cyanide or alkyl isocyanide.
Explanation:
The nucleophile that can attack through two different sites is called an ambident nucleophile.
(1) SCN-,

• It is an ambient nucleophile.
• SCN-, has two attacking centres i.e.. C and N.
• In the Nucleophilic substitution reactions of Alkyl halides, it will give a mixture of alkyl isothiocyanate or alkyl thiocyanate (R-NCS or R-SCN)

(2) RO-,

• It is not an ambient nucleophile.
• RO^-, has only one attacking centre i.e.. O only.
• In the Nucleophilic substitution reactions of Alkyl halides, it will give R-O-R only.

(3) CN- ,

• It is an ambient nucleophile.
• CN-, has two attacking centres i.e.. C and N.
• In the Nucleophilic substitution reactions of Alkyl halides, it will give a mixture of alkyl cyanide or alkyl isocyanide. (R-CN or R-NC)

(4),

• It is an ambient nucleophile.
• has two attacking centres i.e.. O and N.
• In the Nucleophilic substitution reactions of Alkyl halides, it will give a mixture of alkyl nitrile or nitroalkane
  .

Conclusion:
Therefore, In the Nucleophilic substitution reactions of Alkyl halides, RO^-nucleophile cannot act as an ambident nucleophile as it is having only one attacking centre.

The reaction R−OH + HX → RX + H₂​O is a nucleophilic substitution reaction where the reactivity of R−OH will depend upon the stability of carbocation that is formed during the reaction via the S_N​1 mechanism.
S_N1 reaction-

• S_N1 reaction mechanism follows a step-by-step process wherein first, the carbocation is formed from the removal of the leaving group.
• Then the carbocation is attacked by the nucleophile. Finally, the deprotonation of the protonated nucleophile takes place to give the required product.
• The rate-determining step of this reaction depends purely on the electrophilicity of the leaving group and is not impacted at all by the nucleophile.
• The carbocation intermediate formed in step 1 of the S_N1 reaction mechanism is an sp² hybridized carbon. Its molecular geometry is trigonal planar, therefore allowing for two different points of nucleophilic attack, left and right.

S_N1 reaction involves the formation of a carbocation intermediate. More the stability of carbocation more is the reactivity towards S_N1 reaction.
Tertiary carbocations are more stable due to the positive Inductive effect of alkyl groups then secondary and the least stable is primary carbocation.
The reactivity of alcohols will follow the order Tertiary alcohol > secondary alcohol > primary alcohol.

• Any chemical molecule in which two oxygen atoms are linked together by a single covalent bond is known as peroxide linkage.

• Out of the given four molecules, only is having -O-O- linkage.
  • Two oxygen atoms are joined together by a single covalent bond.

Hence, the correct answer to this question is - .

Free expansion ⇒ P_ex = 0
∴ w = - P_ex ΔV = 0
∵ Adiabatic process ⇒ q = 0
also, ΔU = q + w [ first law of thermodynamics]
∴ ΔU = 0
∵ Internal energy of an ideal gas is a function of temperature
∴ If internal energy remains constant
∴ ΔT = 0
So, for free expansion of an ideal gaseds under adiabatic condition is q = 0, ∆T = 0 and w = 0.
Hence, the correct answer is option 3.

Concept:
Esterification reaction -

• It is a reaction between an organic acid (RCOOH) with a primary alcohol(ROH) in presence of an acid to give an ester.
• The reaction is named as esterification as an ester is formed as a result of the reaction.
• It can be represented as -
• The esterification reaction is widely used in the manufacturing of ester for medicinal purposes.
• The esterification reaction is the reverse of the saponification reaction.

Explanation:
Identify ‘A’ in the following reaction :


The given reaction is an Esterification reaction.
→ Esterification reaction of carboxylic acid and alcohol yields in the formation of an ester.
In the given reaction, the product is ethyl ethanoate or ethyl acetate, which is formed when acetic acid and ethanol react in the presence of an acid.
∴ 'A' in the given reaction must be acetic acid.
The complete reaction can be shown as -

Conclusion:
Therefore, 'A' in the given reaction must be acetic acid or CH₃COOH.
Hence, the correct answer is option 2.

Content:

• Benzene and other aromatic compounds show characteristic electrophilic substitution reactions.
• In this reaction, a hydrogen atom of the aromatic ring is substituted by an electrophile.
• The substitution takes place by addition- elimination mechanism.

Mechanism:

• In the first step, the benzene ring donates pi electrons to the electrophile.
• One of the carbon atoms forms a bond with the electrophile.
• In the second step, the complex formed then loses a proton from the saturated carbon atom with the help of a base.
• The aromatic ring is finally regenerated in the last step.
• The products formed in the reaction depend on the substituents called directing groups attached to it.

Explanation:

• Benzene reacts with Carbon monoxide and HCl gas to undergo formylation of benzene.
• The electrophile here is H-C(+)=O and the reaction is an electrophilic substitution reaction.
• The reaction is called the Gatterman Koch reaction and the reaction proceeds as follows:
• The first step is the generation of the electrophile.
• The second step is the donation of the pi-electron density of benzene to the electrophile.
• The aromatic ring is finally regenerated in the last step.

The net reaction is the formation of benzaldehyde.
Hence, Benzene reacts with CO and HCl under pressure to form C₆H₅CHO.

Concept:

• The inert pair effect is a prominent character of the p-block element.
• The term inert pair effect is often used in relation to the increasing stability of oxidation states that are two less than the group valency for the heavier elements of groups 13, 14, 15, and 16.
• The name suggests that the outermost s electrons are more tightly bound to the nucleus in these atoms, and therefore more difficult to ionize or share.

Explanation:

• the p-block elements of the 4th, 5th and 6th periods come after d-block elements, but the electrons present in the intervening d- (and f-) orbitals do not effectively shield the s-electrons of the valence shell.
• As a result, the inert pair of ns electrons remains more tightly held by the nucleus and hence participates less in bond formation.
• Due to the inert pair effect, group-13 elements () show +3 and +1 oxidation states in their compounds. The stability order of these oxidation states will be as,
• +3 oxidation states
• B³⁺ > ql³⁺ > Ga³⁺ > ln³⁺ > Ti³⁺
• B³⁺ does not exist in free states.
• +1 oxidation states
• B⁺ < A⁺ < Ga⁺ < In⁺ < TI⁺b
• B⁺ does not have to exist in ionic as well or covalent compounds.

Hence it is due to the inert pair effect.

The correct answer is Al₂O_3.
Key Points:

• Compounds that lose protons or accept two electrons in solution are known as acids.
• Bases are substances that either gain or lose two electrons.
• Oxides that react with both bases and acids are referred to as amphoteric oxides.
• It has both acidic and basic characteristics, in other words.
• Since they react with both acids and bases, zinc and aluminium, for instance, are both metals, but their oxides, ZnO and Al₂O₃, are amphoteric oxides.
• Other examples are:
  • SnO. [Tin(II) oxide (stannous oxide)].
  • ZnO. [Zinc oxide].
  • PbO. [Lead oxide].

Additional Information:

• Amphoteric material is a material that can react with both acids and bases, typically resulting in the production of salt and water. Because of this, aluminum oxide can react with both acids and bases.
• We shall use its reaction with hydrochloric acid (a strong acid) and sodium hydroxide as an example (a strong base).
• Aluminum oxide either behaves like an acid or a base when combined with these two chemicals or like an acid and a base.
• The reactions are as follows:
  • Al₂O₃ + 6 HCL→ 2 AlCl₃ + 3 H₂O (acts like a base)
  • Al₂O₃ + 2 NaOH + 3 H₂O → 2 NaAl(OH)₄ (acts like an acid).

The correct answer is 0.25 g per gram of water.

Concept:

• Solution: A homogenous mixture of two or more substances. It has two components solute and solvent.
• Solute: The substance that is dissolved in the solvent.
• Solvent: The substance in which solute is dissolved.

For example, in a salt solution, salt is solute and water is solvent.

Explanation:

Solubility:

The maximum amount of a solute that can be dissolved in 100 g of a solvent at a specified temperature is known as the solubility of that solute in that solvent (at that temperature).

Given: Mass of sugar (solute) = 62.5 g

Mass of water (solvent) = 250g

Solubility = (Mass of solute / mass of solvent) × 100

=

= 25 % or 25/100 = 0.25 g per gram of water

Concept:

d-d transition -

• It is the excitation of d-electrons from lower energy d-orbitals to high energy d-orbitals by absorbing a suitable wavelength of energy.
• In the case of octahedral complexes, d orbitals are divided into two sets of energy orbitals t_2g and e_g orbitals. Transitions between these two sets of orbitals are termed as d-d transitions.
• There are some condition or rule which decides the transition is either allowed or forbidden. Such a few conditions are -
  • d-orbital must be partially filled.
  • Centrosymmetric complexes are forbidden for d-d transition.

Paramagnetic complexes - The complexes having unpaired electrons and are weakly attracted by the external magnetic field are called paramagnetic substances. So, the number of unpaired electrons are responsible for the paramagnetism in the complexes.

Explanation:

The d-d transition is shown by the partially filled d-orbitals and the no. of unpaired electrons in that d orbitals give the paramagnetism.

So, Calculating the unpaired electrons in given ions-

⇒ CrO₄2– ⇒

• Cr⁶⁺ = [Ar] 3d⁰
• Unpaired electron (n) = 0
• No unpaired electron means it is diamagnetic.

⇒ Cr₂O₇^2– ⇒

• Cr6+ = [Ar] 3d0
• Unpaired electron (n) = 0
• No unpaired electron means it is diamagnetic.

⇒ MnO₄^2– =

• Mn⁶⁺ = [Ar] 3d¹
• Unpaired electron (n) = 1
• 1 unpaired electron, so, it is Paramagnetic.

⇒ MnO₄^– =

• Mn⁷⁺ = [Ar]
• Unpaired electron (n) = 0
• Hence, Diamagnetic.

As only Cr2O72–, has partially filled d-orbitals and also 1 unpaired electron which makes d-d transition allowed and also it is paramagnetic.

∴, the correct answer is option 3.

For an acidic buffer, the pH can be determined as,

[salt],[acid] is the molarity of the respective salt and acid.
Given data and Calculation-
50 mL of 0.1 M CH3COOH is added to 25 mL of 0.1 M NaOH.
CH₃COOH + NaOH → CH₃COONa + H₂O
Total volume = 50 + 25 =75 mL
Number of millimoles of NaOH present = 25 × 0.1 = 2.5 mMol
Number of millimoles of CH3COOH added = 50 × 0.1 = 5 mMol
After partial neutralisation, [CH3COOH] =
[CH3COONa] = 2.5/75 = 0.033 M

pH = 5 - 0.248 = 4.75