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All questions of Some Basic Concept of Chemistry for NEET Exam

Number of significant figures in 0.001520 is:
a)4
b)7
c)6
d)3
Correct answer is 'A'. Can you explain this answer?

Shruti Mehta answered
All non-zero digits are significant. Zeros before the decimal point are not significant. Zeros to the right of the decimal point are significant.
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Can you explain the answer of this question below:

Molecular mass of glucose molecule (C6H12O6) is:

  • A:

     180 g 

  • B:

    172 g 

  • C:

    182 g 

  • D:

    192 g

The answer is a.

Samridhi Kaur answered
Molecular mass : The sum of the atomic masses of all the atoms in a molecule of a substance is called the molecular mass of the molecule.
Generally we use relative atomic masses of atoms for calculating the molecular mass of 1 mole of any molecular or ionic substances.
Molecular formula of glucose is C6H12O6
Atomic mass of H = 1
Atomic mass pf C = 12
Atomic mass of O = 16
Molecular mass of C6H12O6 = 12(Atomic mass of Hydrogen) + 6(Atomic mass of carbon) + 6(Atomic mass of oxygen)
= 12 x 1 + 6X12 + 6X16
= 12 + 72 + 96 = 180 u.

If we add the numbers 6.68 and 0.8, the result will be:​
  • a)
    7.4
  • b)
    7.5
  • c)
    7.58
  • d)
    7.48 
Correct answer is option 'B'. Can you explain this answer?

Simran Mishra answered
During addition, the result cannot have more digits to the right of the decimal point than either of the original numbers. Since there is only 1 digit after the decimal point in 0.8 so the result 7.48 should be rounded off to 1 decimal point i.e. 7.5.

The scientific notation for 0.00016 is:​
  • a)
    1.6 Χ 10-4
  • b)
    16 Χ 10-4
  • c)
    1.6 Χ 10-2
  • d)
    1.6 Χ 104
Correct answer is option 'A'. Can you explain this answer?

Arya Dasgupta answered
Here, the decimal has to be moved four places to the right side and hence -4 is the exponent in the scientific notation.

Which of the following options is not correct?
  • a)
    2.300 + 0.02017 + 0.02015 = 2.340
  • b)
    126,000 has 3 significant figures
  • c)
    15.15 μs = 1.515 x 10-5 s
  • d)
    0.0048 = 48 x 10-3
Correct answer is option 'D'. Can you explain this answer?

Dev Patel answered
Rule: The result of an addition or subtraction is reported to the same number of decimal places as present in number with the least decimal places.
Since the least precise number is 2.300 and that has three digits after the decimal, therefore the result of the above addition is rounded off to three decimal figures as 2.340.
126,000 has 3 significant figures as zeros are not counted
15.15μs = 15.15×10−6 s = 1.515×10−5 s
0.0048 = 4.8×10−3
Hence, the correct option is D.

Can you explain the answer of this question below:
Number of nitrogen atoms present in 1.4 g of N2:​
  • A:
    6.023 X 1022
  • B:
    6.023 X 1023
  • C:
    3.012 X 1023
  • D:
    3.012 X 1022
The answer is a.

Raghav Bansal answered
Given weight of N₂ gas = 1.4 g
Molar mass of N₂ gas = 28 g
So, mole = given mass/ molar mass
⇒ mole = 1.4/28 = 1/20 mole
Now, number of molecules = mole × avogadro number
⇒ number of molecules = 1/20 × 6.022 × 10²³
⇒ number of molecules = 3.011 × 10²²
Now, we are asked for number of atoms. In N₂, there are 2 atoms, so to obtain number of atoms we will multiply with 2 in number of molecules.
⇒ number of atoms = 2 × 3.011 × 10²²
⇒ number of atoms = 6.022 × 10²²

What is the mass of 0.20 mole of C2H5OH (ethanol)?​
  • a)
    46 g
  • b)
    23 g
  • c)
    4.6 g
  • d)
    none of these
Correct answer is option 'D'. Can you explain this answer?

Neha Joshi answered
Molecular Mass of Ethanol
= 2(12) + 5 (1) + 16 + 1 
= 24 + 5 + 17 
= 46
Now,
Moles (n) = Given Mass (m)/Molecular Mass (M)
Thus, to = nM
= (0.2) (46)
= 9.2

Which law is also known as Law of constant composition?
  • a)
    Law of multiple proportions
  • b)
    Avogadro’s law
  • c)
    Law of conservation of mass
  • d)
    Law of definite proportions
Correct answer is option 'D'. Can you explain this answer?

Pooja Shah answered
The law of definite proportions, also known as the law of constant composition states that all pure samples of the same chemical compound contain the same elements combined in the same proportions by mass.
What this law emphasizes is that, if pure samples of the same chemical substance, wherever they may be found, are analyzed, it will be found that they all consist of the same elements, as well as having these elements combine in the same proportions by mass.
For examples, pure sample of copper(II) oxide is composed of copper and oxygen, in the proportion of 1:1 by mole, or 64 g of copper to 16 g of oxygen or 1 g of copper to 0.25 g of oxygen. 

What is the empirical formula of C2H2 and C6H6?​
  • a)
    C6H6
  • b)
    C2H2
  • c)
    CH
  • d)
    C3H3
Correct answer is option 'C'. Can you explain this answer?

Krishna Iyer answered
Empirical formula represents the simplest whole number ratio of various atoms in a compound hence for both C2H2 and C2H6 the empirical formula is CH.

Can you explain the answer of this question below:

Molar mass of F2 is 38 g. How many atoms are present in 0.147 mole of F2?​

  • A:

    6.02 Χ 1023 atoms

  • B:

    8.78 Χ 10222 atoms

  • C:

    0.292 atoms

  • D:

    1.76 Χ 1023 atoms

The answer is d.

Puja Das answered
One molecule of F2  contains 2 atoms of fluorine.
1 mol of fluorine contains 2 X 6.023 X 1023 atoms
So, 0.147 moles will contain 0.147 X 2 X 6.023 X 1023 = 1.76 X 1023 atoms of flourine.

Volume of 17g of NH3 at N.T.P. will be​
  • a)
    22.4 L
  • b)
    2.24 L
  • c)
    4.48 L
  • d)
    44.8 L
Correct answer is 'A'. Can you explain this answer?

Neha Sharma answered
Molar mass of NH3 is 17g. So the volume of 17g of NH3 i.e 1 mole NH3 at N.T.P. will be 22.4L.

The ‘Candela’ is the unit of:
  • a)
    Luminous intensity
  • b)
    Amount of substance
  • c)
    Thermodynamic temperature
  • d)
    Electric curren
Correct answer is option 'A'. Can you explain this answer?

Anjana Sharma answered
The SI unit of luminous intensity is the candela , which is a primary unit. The derived SI unit of luminous flux is the lumen (abbreviated lm). These are based on the sensitivity of the human eye to light. Light sources are often evaluated based on their luminous efficacy, which is defined as the luminous flux divided by the power consumed and is measured in lm W−1. In a physical or online store, find manufacturer’s specifications for representative incandescent, halogen, high-temperature-discharge, LED, and fluorescent lamps of similar luminous flux and compare their luminous efficacy.

The maximum number of molecules is present in
  • a)
    15 L of H2 gas at STP [2004]
  • b)
    5 L of N2 gas at STP
  • c)
    0.5 g of H2 gas
  • d)
    10 g of O2 gas
Correct answer is option 'A'. Can you explain this answer?

Hansa Sharma answered
No. of molecules in different cases:
(a) 22.4 litre at STP contains = 6.023×1023 molecule of H2
∴ 15 litre at STP contains molecules
(b) 22.4 litre at STP contains = 6.023×1023 molecule of N2
∴ 5 litre at STP contains molecules
(c) 2 gm of  H2 = 6.023×1023 molecules of  H2
∴ 0.5 gm of H2 contains molecules
(d) Similarly, 10 g of O2 gasmolecules
Thus (a) will have maximum number of molecules

For the reaction 
224 g of CO is available to react with 400 g Fe2O3, the yield of iron and CO2, are:
  • a)
    225 and 279
  • b)
    280 and 330 g
  • c)
    210 and 290
  • d)
    210 and 279 g
Correct answer is 'B'. Can you explain this answer?

Neha Sharma answered
Moles of CO =8 moles Moles of Fe2O3= 2.5 moles.
3 moles of CO is needed for 1 mole of Fe2O3 so 8 moles of CO will require 2.66 mole of Fe2O3 so Fe2O3 is limiting reagent.
1 mole of Fe2O3 produce 2 mole of Fe so 2.5 mole of Fe2O3will produce 5 mole of Fe = 280g of Fe.
Also 1 mole of Fe2O3 also produce 3 mole of CO2 so 2.5 mole of Fe2O3 will produce 7.5 mole of CO2=330g.

The number of significant figures in 3256 is:
  • a)
    4
  • b)
    3
  • c)
    5
  • d)
    2
Correct answer is option 'A'. Can you explain this answer?

Lohit Matani answered
  • The significant figures of numbers are digits to convey the meaning that contributes to its measurement resolution.
  • Non-zero digits are always significant.
  • Here, 3256, this number has four non-zero numbers.
  • That's why it has four significant figures.

Law of conservation of mass was given by:
  • a)
    Avogadro
  • b)
    Antoine Lavoisier
  • c)
    John Dalton
  • d)
    Joseph Proust
Correct answer is option 'B'. Can you explain this answer?

Lavanya Menon answered
The Law of Conservation of Mass (or Matter) in a chemical reaction can be stated thus:
In a chemical reaction, matter is neither created nor destroyed.
It was discovered by Antoine Laurent Lavoisier (1743-94) about 1785. However, philosophical speculation and even some quantitative experimentation preceeded him. In addition, he was certainly not the first to accept this law as true or to teach it, but he is credited as its discoverer.

An oxide of metal M has 40% by mass of oxygen. Metal M has relative atomic mass of 24g/mol. The empirical formula of the oxide is:​
  • a)
    M2O5
  • b)
    M2O
  • c)
    M2O3
  • d)
    MO
Correct answer is option 'D'. Can you explain this answer?

Nandini Patel answered
40% by mass oxygen means 40 g of oxygen
So, amount of metal in metal oxide=60 g
Now, The empirical formula can be given as 40/16 : 60/24 = 2.5 : 2.5 = 1:1
Therefore, the empirical formula is MO

The SI unit of time is:
  • a)
    minute
  • b)
    metre
  • c)
    second
  • d)
    kilogram
Correct answer is option 'C'. Can you explain this answer?

Krishna Iyer answered
The SI unit of time, the second, symbols, is easy enough to define, but time itself can only be defined in reference to other quantities.

Can you explain the answer of this question below:

The number of significant figures in 3.1205 are

  • A:

    3

  • B:

    7

  • C:

    6

  • D:

    5

The answer is d.

Arpita Nambiar answered
The answer is 5 because all non zero digits and zero between the non zero digits are significant.

Which of the following compounds has the same empirical formula as that of glucose (C6H12O6)?​
  • a)
    CH3COOH
  • b)
    CH3CHO
  • c)
    CH3OH
  • d)
    C2H6
Correct answer is 'A'. Can you explain this answer?

Naveen Chavan answered
The empirical formula of a chemical compound is the simplest positive integer ratio of atoms present in a compound.
Molecular formula of glucose is C6H12O6.
Its empirical formula is CH2O.
For CH3COOH, the empirical formula is also CH2O.

What will be the molality of the solution containing 18.25 g of HCl gas in 500 g of water?
  • a)
    0.1 m
  • b)
    1 M
  • c)
    0.5 m
  • d)
    1 m
Correct answer is option 'D'. Can you explain this answer?

Saikat Sharma answered
Given:
Mass of HCl = 18.25 gm
Molar mass of HCl = 36.5 g/mol
Mass of water = 500 gm
                     = 0.5 kg
No. of moles of HCl;
 
Molality is,
Molality of solution is 1 m.

Can you explain the answer of this question below:
The number of base SI units is:
  • A:
    5
  • B:
    7
  • C:
    6
  • D:
    2
The answer is b.

Om Desai answered
Base system means fundamental physical quantities and there are 9 fundamental physical quantities but only 7 have units so number of base SI units is 7.

Number of significant figures in 0.001520 is:
  • a)
    0
  • b)
    7
  • c)
    6
  • d)
    3
Correct answer is option 'A'. Can you explain this answer?

Raghav Chakraborty answered
All non-zero digits are significant. Zeros before the decimal point are not significant. Zeros to the right of the decimal point are significant.

If you have 2 moles of A and 3 moles of B, Identify the limiting reagent in the following reaction.
A + B → AB​
  • a)
    A
  • b)
    B
  • c)
    A as well as B
  • d)
    None
Correct answer is option 'A'. Can you explain this answer?

Suresh Reddy answered
A + B → AB divide given moles of each reactant by their stoichiometric coefficient , the one with least ratio is limit reagents divide with their co efficient A=2/1 =2 B=3/1 =3. So A is the limiting reagent.

The distinction between atoms and molecules was made by:
  • a)
    Dalton’s atomic theory
  • b)
    Avogadro law
  • c)
    Laws of chemical combination
  • d)
    Gay lussacs law
Correct answer is 'B'. Can you explain this answer?

Preeti Iyer answered
Avogadro made the distinction between atoms and molecules, which today seems clear. However, Dalton rejected Avogadro's hypothesis because Dalton believed that atoms of the same kind could not combine. Since it was believed that atoms were held together by an electrical force, only unlike atoms would be attracted together, and like atoms should repel. Therefore it seemed impossible for a molecule of oxygen, O2, to exist. Avogadro's work, even if it was read appears not to have been understood, and was pushed into the dark recesses of chemistry libraries and ignored. Avogadro continued to teach at the university of Turin, when it was not closed because of the political upheavals going on in Italy at the time, and died in 1854, an unknown figure. 

Laws of chemical combinations can be explained on the basis of:
  • a)
    Avogadro law
  • b)
    Gay lussacs law
  • c)
    Dalton’s atomic theory
  • d)
    Mole concept
Correct answer is option 'C'. Can you explain this answer?

Gaurav Kumar answered
The old ideas were put on a scientific scale by John Dalton in the form of a theory, known as Dalton’s atomic theory,
Main postulates of which are as follows :
• All matters are made of atoms. Atoms are indivisible and indestructible.
• All atoms of a given element are identical in mass and properties.
• Atoms of different elements differ in properties and have different masses and sizes.
• Compounds are formed by a combination of two or more different kinds of atoms.
• A chemical reaction is a rearrangement of atoms.These are neither created nor destroyed in a chemical reaction

What is incorrect about the Law of conservation of mass?
  • a)
    A given compound always conatains exactly the same proportion of elements by weight
  • b)
    Mass of reactants is equal to the mass of products
  • c)
    Matter can neither be created nor destroyed
  • d)
    It was given by Antoine Lavoiser
Correct answer is option 'A'. Can you explain this answer?

Jyoti Kumar answered
The law of definite proportions, also known law of definite composition, states that regardless of the amount, a pure compound always contains the same elements in the same proportions by mass. Law of multiple proportions, also known as Dalton s Law, states that when one element combines with another to form more than one compound, the mass rations of the elements in the compounds are simple whole numbers of each other.

How many atoms of hydrogen are in 67.2 L of H2 at STP?
  • a)
    5.612 × 1024
  • b)
    2.612 × 1024
  • c)
    4.612 × 1024
  • d)
    3.6132 × 1024 
Correct answer is option 'D'. Can you explain this answer?

Anjana Sharma answered
Standard temperature and pressure (STP) is defined as 0 degrees Celsius and 1 atmosphere of pressure. At STP, 1 mole of any gas occupies 22.4 liters.
First, calculate the number of moles of hydrogen gas (H2) in 67.2 liters:
67.2 L / 22.4 L/mole = 3 moles of H2
Each molecule of H2 contains 2 atoms of hydrogen. Therefore, 3 moles of H2 contains:
3 moles * (6.022 x 10^23 molecules/mole) * 2 atoms/molecule = 3.6132 x 10^24 atoms of hydrogen.

The correct relationship between picometer and nanometer is
  • a)
    1nm = 1000pm
  • b)
    1nm = 10pm
  • c)
    1pm = 10nm
  • d)
    1pm = 100nm
Correct answer is option 'A'. Can you explain this answer?

Neha Joshi answered
1 picometer = 10-12 m
1 nanometer=10-9 m
So, 1 picometer = 0.001 nanometer .
From this we get 1 nanometer= 1000 picometer.
Hence, the correct answer is Option A.

The unit of amount of substance is:
  • a)
    ampere
  • b)
    second
  • c)
    mole
  • d)
    kilogram
Correct answer is option 'C'. Can you explain this answer?

Pooja Shah answered
  • Amount of Substance is also called as material quantity. The amount of substance refers to a standards-defined quantity that measures the size of an ensemble of elementary entities, such as atoms, molecules, electrons, and other particles.
  • The amount of substance appears in thermodynamic relations such as the ideal gas law, and in stoichiometric relations between reacting molecules as in the law of multiple proportions. The unit symbol of the amount of substance is mole.

Which of the following has more number of atoms?
  • a)
    1 mole of Neon gas
  • b)
    1 mole of Ozone gas
  • c)
    1 mole of Oxygen gas
  • d)
    1 mole of Carbon monoxide gas
Correct answer is option 'B'. Can you explain this answer?

Nandini Iyer answered
Neon's atomicity is 1 Ozone's atomicity is 3 Oxygen's atomicity is 2 Carbon monoxide's atomicity is 2 Now Ozone has more atom in a molecule than any other gas in the options. So in 1 mole or 6.022×1023 Ozone has more atom.

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