basic chemistry

Class 11 Chapter 1 Some Basic Concepts of Chemistry Important mcq with answers and Explanation

Multiple Choice Questions (MCQ’s)

Class 11 Chemistry- Some Basic Concepts of Chemistry Important MCQs
  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


  • 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.


  • 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.


  • 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


  • 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.


  • 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


  • 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


  • 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


  • 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)


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

Answer ) 1/12th 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 1/12th 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


  • 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

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

Answer ) 32 / NA g

Brief Explanation :

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

Mass of one O2 – molecule = 32/NA g


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

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.


  • 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.


  • 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.


  • 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.


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

1.Percent

2.Actual

3.Theoretical

4.All of them

Answer )

Brief Explanation : Theoretical

A theoretical yield of reaction is independent of the reaction conditions because it involves no practical work


  • 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


  • 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.



  • 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


  • 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)


  • 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


  • 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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