Question

The molecular mass of ${\text{Na}}_2{\text{CO}}_3$ is 96 u.

• A. 51
• B. 74

Answer 1

The correct option is B

74

Molecular mass is equal to the sum of the masses of its constituent atoms.
Atomic mass of sodium = 23 u
Atomic mass of carbon = 12 u
Atomic mass of oxygen = 16 u
Therefore, the molecular mass of ${\text{Na}}_2{\text{CO}}_3$
= 2 $\times$ Atomic mass of sodium + 1 $\times$ Atomic mass of carbon + 3 $\times$ Atomic mass of oxygen
= 2 $\times$ 23 + 1 $\times$ 12 + 3 $\times$ 16
= 46 +12+ 48
= 106 u