20 " mL of " a gasous bydrocarbon (A) was exploded with excess of `O_2` in an eudiometer tube. On cooling, the volume was reduced by 50 mL. On further treatment with KOH, there was further contraction of 40 mL. The molecular formula of the hydrocarbon A is
(a). `C_2H_6`
(b). `C_2H_4`
` C_3H_6`
(d). `C_3H_8`

Explanation

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

### Step 1: Understand the combustion reaction
The combustion of a hydrocarbon (CxHy) in the presence of excess oxygen (O2) produces carbon dioxide (CO2) and water (H2O). The reaction can be represented as:
\[ \text{CxHy} + \frac{x + y/4}{O_2} \rightarrow x \text{CO2} + \frac{y}{2} \text{H2O} \]

### Step 2: Analyze the initial conditions
We start with 20 mL of the hydrocarbon A. Therefore, the initial volume of the gas before combustion is:
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