Determine the formula unit mass of the following substances.

(A) Ammonium nitrate (NH₄NO₃), used as a nitrogen fertiliser, which is essential for plant growth.

(B) Phosphoric acid (H₃PO₄), used to make phosphate fertiliser and detergents.

(C) Sodium hydrogencarbonate (NaHCO₃), used to relieve acidity and helps in digestion.

The formula unit mass of a substance is calculated by adding the atomic masses of all the atoms present in its formula.
Using the atomic mass: H = 1 u, C = 12 u, N = 14 u, O = 16 u, Na = 23 u, P = 31 u, the formula unit mass of the given substances are calculated as follows:
(A) Ammonium nitrate (NH₄NO₃):

$$\begin{aligned} \text{Formula unit mass} &= (14 \times 1) + (1 \times 4) \\ &+ (14 \times 1) + (16 \times 3) \\ &= 14 + 4 + 14 + 48 \\ &= 80 \text{ u} \end{aligned}$$

(B) Phosphoric acid (H₃PO₄):

$$\begin{aligned} \text{Formula unit mass} &= (1 \times 3) + (31 \times 1) \\ &+ (16 \times 4) \\ &= 3 + 31 + 64 = 98 \text{ u} \end{aligned}$$

(C) Sodium hydrogencarbonate (NaHCO₃):

$$\begin{aligned} \text{Formula unit mass} &= (23 \times 1) + (1 \times 1) \\ &+ (12 \times 1) + (16 \times 3) \\ &= 23 + 1 + 12 + 48 \\ &= 84 \text{ u} \end{aligned}$$