15 " mL of " a gaseous hydrocarbon A requried for complete combustion. 357 " mL of " air `(21%` oxygen by volume) and gaseous products occupied 327 mL (all volumes being measured at STP. The molecular formula of the hydrocarbon A is
(a). `C_2H_6`
(b). `C_2H_4`
(c). `C_3H_6`
(d). `C_3H_6`

Explanation

To determine the molecular formula of the gaseous hydrocarbon A, we can follow these steps:

### Step 1: Identify the volume of oxygen required for combustion
Given that 357 mL of air contains 21% oxygen, we can calculate the volume of oxygen in the air.

\[ \text{Volume of } O_2 = \frac{21}{100} \times 357 \text{ mL} = 74.97 \text{ mL} \]
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