Assertion (A): Atomic mass is expressed in atomic mass unit.

Reason (R): Atomic mass is defined as $\dfrac{1}{12}$ times the mass of carbon-12.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Assertion (A): Sulphur is an octatomic molecule.

Reason (R): The number of atoms in a molecule of an element is known as atomicity.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Complete the following blanks in the equation as indicated.

CaH₂ (s) + 2H₂O (aq) ⟶ Ca(OH)₂ (s) + 2H₂ (g)

(a) Moles: 1 mole + …………… ⟶ …………… + ……………

(b) Grams: 42g + …………… ⟶ …………… + ……………

(c) Molecules: 6.02 x 10²³ + …………… ⟶ …………… + ……………

Correct the statements, if required

(a) One mole of chlorine contains 6.023 × 10²³ atoms of chlorine.

(b) Under similar conditions of temperature and pressure, two volumes of hydrogen combined with two volumes of oxygen will give two volumes of water vapour.

(c) Relative atomic mass of an element is the number of times one molecule of an element is heavier than $\dfrac{1}{12}$ the mass of an atom of carbon [C¹²].

(d) Under the same conditions of the temperature and pressure, equal volumes of all gases contain the same number of atoms.