Multiple Choice Questions (MCQ’s)

1. The simplest form of pure matter is
   1. Aqua Regia
   2. Natural Gas
   3. Metallic Copper
   4. Bleaching Powder

Answer ) Metallic copper

Brief Explanation :

Metallic copper is the simplest form of pure matter, which consists of the same kind of copper atoms having the same atomic numbers and same chemical properties

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• An impure matter of the following is:
  1. Coke
  2. Water
  3. Table Salt
  4. Concrete

Answer ) Concrete

Brief Explanation :

Concrete is an impure matter because it is a mixture of gravels, sand and cement.

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• A process that represents a physical change, is
  1. Oxidation
  2. Reduction
  3. Sublimation
  4. Rusting of Iron

Answer ) Sublimation

Brief Explanation :

Sublimation is a physical change during which volatile solid changes directly into vapor state without melting, The chemical composition and chemical properties remains same.

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• The fundamental property and identity of an element is
  1. Atomic mass
  2. Mass number
  3. Atomic number
  4. Average atomic mass

Answer ) Atomic number

Brief Explanation :

Atomic number is a fundamental property and identity of an element. The properties of an element depend upon their atomic number, Different elements have always different atomic numbers

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• A species that contains one proton, one neutron and two electron is
  1. H^-1
  2. D^-1
  3. He
  4. He⁺²

Answer ) D^-1 ( Deuterium )

Brief Explanation :

Deuterium atom has one electron, one proton and one neutron. Thus D^-1 ion wills one contains one proton, one neutron and two electrons.

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• A substance that can be separated into components only by chemical method?
  1. Air
  2. Petroleum
  3. Bleaching Powder
  4. Molten NaCl

Answer ) Molten NaCl

Brief Explanation :

Molten NaCl is a chemical compound and chemical compound can be separated into its components by chemical methods like electrolysis

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• Atoms which are chemically same and differ only in mass-dependent properties are
  1. ₆C¹² , ₆C¹³ , ₆C¹⁴
  2. ₁H¹ , ₂He⁴ , ₆C¹²
  3.  ₁₄Si³⁰ , ₁₅P³¹ , ₁₆S³²
  4. ₁₈Ar⁴⁰ , ₁₉K⁴⁰ , ₂₀Ca⁴⁰

Answer ) ₆C¹² , ₆C¹³ , ₆C¹⁴

Brief Explanation :

₆C¹² , ₆C¹³ , ₆C¹⁴ are isotopes having the same atomic numbers but different mass numbers. Isotopes have the same chemical property due to same atomic number but different mas dependent physical properties and rates of reactions due to different mass number

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• Elements are arranged in periodic table, in increasing order of their
  1. Valency
  2. Mass Number
  3. Oxidation State
  4. Charge on nucleus

Answer ) Charge on nucleus

Brief Explanation :

Atomic number (charge on Nucleus) is the fundamental property and elements in the periodic table have been arranged in order of their increasing atomic numbers

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• H₂O, CH₄, HF and Na⁺¹ have the same
  1. Number of protons
  2. Number of electrons
  3. Number of neutrons
  4. Average mass

Answer ) Number of electrons

Brief Explanation :

H₂O, CH₄, HF and Na⁺¹ ions, all have the same number of electrons (10)

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• One atomic mass unit (a.m.u) stands for
  1. One C¹² atom
  2. One H-atom
  3. 1/12^th of the mass of H-atom
  4. 1/12^th of the mass of C¹²-atom

Answer ) 1/12^th of the mass of C¹²-atom

Brief Explanation :

1 a.m.u = 1.66 x 10^-24 g

Mass of 6.023 x 10²³ C¹² atoms = 12 g

Mass of one C¹² atom = 12 x 1 /6.023 x 10²³

                                        = 1.9927 x 10^-23 g

We have one atomic mass unit is 1/12^th of the mass of C¹² atoms

1 amu    = 1 /12 x mass of C¹² atom

1 amu    = 1 /12 x 1.9927 x 10^-23 g

               = 1.66 x 10^-24g

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• One mole of NaCl contains6.02×10²³
  1. Ions
  2. Atoms
  3. Molecules
  4. Formula Unit

Answer ) Formula Unit

Brief Explanation :

• One mole of Sodium Chloride contains 6.023 x 10²³ NaCl Formula units

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• Mass of one mole of oxygen is
  1. 32 g
  2. 16 x N_A g
  3. 32 x N_A g
  4. 32 / N_A g

Answer ) 32 / N_A g

Brief Explanation :

Mass of N_A (6.023 x 10²³) O₂ – molecules = 32g

Mass of one O₂ – molecule = 32/N_A g

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• Number of atoms in 64 a. m. u. of SO₂ is
  1. 3
  2. 64
  3. 3 x N_A
  4. 64 x N_A

Answer ) 3

Brief Explanation :

64 a.m.u. is the mass of one molecule of SO2 and thus contains three (3) atoms. However 64 g is the mass of one mole of SO2 molecule and contains 3 x 6.023 x 10²³atoms.

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• A balanced chemical equation may not obey
  1. Law of conservation of mass
  2. Law of conservation of volume
  3. Law of constant composition
  4. All of these

Answer ) Law of conservation of volume

Brief Explanation :

In a balanced chemical equation, each compound has definite composition with correct chemical formula. The total mass of reactants is always equal to total mass of products in balanced equation. However, volumes of reactants and products may not be equal. Thus balanced equation obeys the law of conservation of mass and law of definite proportion but may or may not obey the law of conservation of volume.

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• The limiting reactant in a chemical reaction is
  1. Is used up earlier and completely
  2. Controls the yield of reaction
  3. Gives the least amount of product
  4. All of these

Answer ) All of these

Brief Explanation :

A limiting reactant in a chemical reaction is always used up earlier, gives the least amount of product and controls the yield of reaction. It is present in lesser amount than the required stoichiometric amount.

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• When equal moles of the reactant react together, the limiting reactant is

1. K₂Cr₂O₇
2. HCl
3. Cl₂
4. None

Answer ) HCl

Brief Explanation :

K₂Cr₂O₇ + 14 HCl to form 3Cl₂ + other products. Let’s one mole of each reactant takes part in a chemical reaction.

One mole of K₂Cr₂O₇ = 3 mole Cl₂

Similarly, 14 moles of HCl = 3 mole Cl₂

1 mole of HCl = 3/14 mole of Cl₂

As 1 mole of HCl produces the least amount of Cl₂ product so HCl is a limiting reactant.

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• A yield of reaction that is independent of their reaction conditions is

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• The yield of reaction is becomes 100% when
  1. Actual yield < Theoretical yield
  2. Actual yield > Theoretical yield
  3. Actual yield ≤ Theoretical yield
  4. Actual yield  = Theoretical yield

Answer ) Actual yield  = Theoretical yield

Brief Explanation :

The yield of reaction is  become 100% when actual yield equal to theoretical yield of reaction

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• Actual yield is always lesser than theoretical yield due to
  1. Lack of optimum reaction conditions
  2. Mechanical loss of reactants and / or products
  3. Reversibility of reaction
  4. All of these

Answer ) All of these

Brief Explanation :

Actual yield is always lesser than theoretical yield due to one or more reason like not availability of reagent and the most suitable reaction conditions; loss of reactants / products during experimental work, reversibility of reaction of by-products formation etc.

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• Mass of Cl^-1 ions in a sample of AlCl₃ that contains 6.023 x 10²³ Al⁺³ ions
  1. 3
  2. 3 x 10²¹
  3. 6.023 x 10²³ / 3
  4. 3 x 6.023 x 10²³

Answer ) 3

Brief Explanation :

From the formula AlCl₃ we have

1 Al⁺³ ions = 3Cl^-1 ion

6.023 x 10²³ Al⁺³ion = 3 x 6.023 x 10²³ Cl^-1 ion

                                         = 3 mole of Cl^-1 ion

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• The simplest ration b/w atoms (Pb:O) of a binary compound of oxygen containing 90.66% lead ₈₂Pb²⁰⁷, is
  1. 1:1
  2. 1:2
  3. 3:4
  4. 9:1

Answer ) 3:4

Brief Explanation :

We have that

Lead (Pb) = 90.66% = 90.66/207 mol = 0.4379 mol

Oxygen (O2) = 100 – 90.66 = 9.34% = 9.34/16 mol = 0.5838 mol

Relative number of atoms of Pb = 0.4379/0.4379 = 1

Relative number of atoms of Oxygen = 0.5838/0.4379 = 1.333

To change number of atoms into whole number, multiplying both the values with 3 i.e.

Atoms of Pb = 1 x 3 = 3

Atoms of Oxygen = 1.333 x 3 = 3.999 ~ 4 Hence the simple ration between Pb and Oxygen is (3:4)

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• When 60cm³ each of H₂ and O₂ reacts together, the theoretical decrease in volume of the reacting gasses will be
  1. 120 cm³
  2. 90 cm³
  3. 60 cm³
  4. 30 cm³

Answer )

Brief Explanation : 90 cm³

From the balanced equation  2H₂ +O₂ to form 2H₂O ,

 We have that 2cm³ of H₂ reacts with = 1 cm³ of O₂

60 cm³ of H₂ reacts with = 60/2 = 30 cm³ of O₂

Total volume of reacting gases = 60+60= 120 cm³

Volume of gases used = 60 cm³ of H₂ + 30 cm³ of O₂ = 90 cm³

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• Moles of fluorine required to reach with 0.6 mole of metal M to form46.8 grams of MF₂
  1. 0.12 mole
  2. 1.00 mole
  3. 1.20 mole
  4. 2.00 mole

Answer )

Brief Explanation : 1.20 mole

• From the formula  MF₂ we have that

1 mole of metal M reacts with = 2 mole Fluorine

 0.6 mole of metal M will reacts with= 2 x 0.6 = 1.2 mole of Fluorine

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