Assertion (A): One litre of hydrogen weighs the same as one litre of oxygen.

Reason (R): One litre of hydrogen contains the same number of molecules as one litre of oxygen.

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): 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): One mole of a gas occupies 24.4 litres at S.T.P.

Reason (R): The mass of one mole of a gas is equal to its molecular mass.

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 + …………… ⟶ …………… + ……………