The absolute density of atmospheric air is measured to be at standard temperature and pressure (STP) — Mole Concept and Some Basic Concepts of Chemistry Chemistry Question

💡 Solution & Explanation

Step 1: Convert absolute density to standard units. $0.001293\text{ g/cm}^3 = 1.293\text{ g/L}$. Step 2: Calculate the average molar mass of air. At STP, $1\text{ mole}$ occupies $22.4\text{ L}$. Molar Mass = $1.293\text{ g/L} \times 22.4\text{ L/mol} = 28.96\text{ g/mol}$. Step 3: Calculate standard vapour density (relative to hydrogen). $V.D. = \frac{\text{Molar Mass}}{2} = \frac{28.96}{2} = 14.48$. Option B is incorrect because air is a mixture, so $28.96$ is its *average* molar mass, not a true molecular weight.