Class 11 Chemistry MCQ – Some Basic Concepts of Chemistry

1. Which of the following is NOT a physical property?

a) Melting point
b) Boiling point
c) Reactivity with acid
d) Density

Answer:

c) Reactivity with acid

Explanation:

Reactivity with acid is a chemical property, not a physical one.

2. The SI unit of mass is:

a) Gram
b) Kilogram
c) Pound
d) Ounce

Answer:

b) Kilogram

Explanation:

The International System of Units (SI) recognizes the kilogram as the base unit of mass.

3. The number of atoms in one mole of carbon is known as:

a) Avogadro's number
b) Faraday's number
c) Atomic number
d) Molar mass

Answer:

a) Avogadro's number

Explanation:

Avogadro's number (6.022 x 10^23) represents the number of atoms in one mole of any substance.

4. What does the term "molar mass" refer to?

a) Mass of one mole of electrons
b) Mass of one molecule
c) Mass of one mole of a substance
d) Mass of the nucleus

Answer:

c) Mass of one mole of a substance

Explanation:

Molar mass is the mass (in grams) of one mole of a substance.

5. Which of the following represents a chemical change?

a) Boiling of water
b) Dissolution of sugar in water
c) Rusting of iron
d) Melting of ice

Answer:

c) Rusting of iron

Explanation:

Rusting is a process wherein iron reacts with moisture and oxygen, leading to a chemical change.

6. How many significant figures are in the number 0.002305?

a) 3
b) 4
c) 5
d) 6

Answer:

b) 4

Explanation:

Leading zeros are not counted as significant. The significant figures are 2305.

7. What is the empirical formula of a compound that has 40% carbon, 6.7% hydrogen, and 53.3% oxygen by weight?

a) CH2O
b) C2H4O2
c) CH3OH
d) C2H5OH

Answer:

a) CH2O

Explanation:

Empirical formula represents the simplest whole-number ratio of the elements in a compound.

8. The atomic number of an element represents:

a) Number of protons
b) Number of neutrons
c) Number of electrons
d) Molar mass

Answer:

a) Number of protons

Explanation:

Atomic number is the number of protons present in the nucleus of an atom.

9. Which of the following is an extensive property?

a) Density
b) Refractive index
c) Temperature
d) Volume

Answer:

d) Volume

Explanation:

Extensive properties depend on the amount of substance present.

10. Isotopes of an element differ in the number of:

a) Protons
b) Electrons
c) Neutrons
d) Quarks

Answer:

c) Neutrons

Explanation:

Isotopes of an element have the same number of protons but different numbers of neutrons.

11. The law that states that matter can neither be created nor destroyed is:

a) Law of Definite Proportions
b) Law of Conservation of Mass
c) Avogadro's Law
d) Gay-Lussac's Law

Answer:

b) Law of Conservation of Mass

Explanation:

This law asserts that the total mass remains constant before and after a chemical reaction.

12. If an element X has two isotopes with atomic masses 35 and 37, and their relative abundance is 3:1, the average atomic mass of X is:

a) 35.5
b) 36
c) 35.25
d) 36.5

Answer:

a) 35.5

Explanation:

Average atomic mass = (35*3 + 37*1) / 4 = 142/4 = 35.5

13. The mass percent of an element in a compound is defined as:

a) (Mass of element/Total mass of compound) x 10
b) (Mass of element/Total mass of compound) x 1000
c) (Mass of element/Total mass of compound) x 100
d) (Total mass of compound/Mass of element) x 100

Answer:

c) (Mass of element/Total mass of compound) x 100

Explanation:

Mass percent gives the percentage by mass of each element in a compound.

14. How many moles are in 22 grams of carbon dioxide (CO2)?

a) 0.25 moles
b) 0.5 moles
c) 1 mole
d) 2 moles

Answer:

b) 0.5 moles

Explanation:

Molar mass of CO2 = 44g/mol. So, 22 grams of CO2 = 22/44 = 0.5 moles.

15. Which of the following is a homogeneous mixture?

a) Sand and salt
b) Water and oil
c) Air
d) Milk and water

Answer:

c) Air

Explanation:

A homogeneous mixture has a uniform composition throughout.

16. The atomic mass of an element is determined relative to the mass of:

a) Hydrogen atom
b) Oxygen atom
c) Carbon-12 atom
d) Nitrogen atom

Answer:

c) Carbon-12 atom

Explanation:

Carbon-12 is taken as the standard reference for determining atomic masses.

17. The volume occupied by one mole of a gas at STP is:

a) 22.4 liters
b) 2.24 liters
c) 11.2 liters
d) 44.8 liters

Answer:

a) 22.4 liters

Explanation:

At standard temperature and pressure (STP), one mole of any gas occupies 22.4 liters.

18. A solution with a pH of 7 is:

a) Acidic
b) Basic
c) Neutral
d) Amphoteric

Answer:

c) Neutral

Explanation:

A pH value of 7 indicates a neutral solution.

19. Which of the following is a scalar quantity?

a) Velocity
b) Force
c) Displacement
d) Mass

Answer:

d) Mass

Explanation:

Scalar quantities have magnitude but no direction.

20. Which postulate of Dalton's atomic theory has been modified?

a) Atoms are indivisible
b) Atoms of the same element are identical
c) Atoms can neither be created nor destroyed
d) Atoms combine in fixed ratios to form compounds

Answer:

a) Atoms are indivisible

Explanation:

With the discovery of subatomic particles, it's now known that atoms can be divided into protons, neutrons, and electrons.

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