The average molar mass of the vapour above solid `NH_4Cl` is nearly `26.5 g "mole"^(-1)` . Find the composition of the vapour.

Explanation

To find the composition of the vapour above solid NH4Cl, we can follow these steps:

### Step 1: Identify the decomposition reaction
The solid ammonium chloride (NH4Cl) decomposes into ammonia (NH3) and hydrogen chloride (HCl) gases:
\[ \text{NH}_4\text{Cl (s)} \rightleftharpoons \text{NH}_3\text{ (g)} + \text{HCl (g)} \]

### Step 2: Define the molar masses
- Molar mass of NH3 = 14 (N) + 3(1) (H) = 17 g/mol
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