Twenty millilitres of a gaseous hydrocarbon required 400 ml of iar for complete cumbustion. The air contains `20%` by explosion and cooling was found to be 380 ml.
Q. volume of residual nitrogen is:

Options

A. 300 ml
B. 310 ml
C. 320 ml
D. 330 ml

Explanation

To solve the problem, we need to find the volume of residual nitrogen after the combustion of a gaseous hydrocarbon. Here are the steps to arrive at the solution:

### Step 1: Determine the volume of oxygen in the air
Given that the air contains 20% oxygen, we can calculate the volume of oxygen in the 400 ml of air used for combustion.

\[ \text{Volume of Oxygen} = \text{Total Volume of Air} \times \text{Percentage of Oxygen} \]
\[ \text{Volume of Oxygen} = 400 \, \text{ml} \times \frac{20}{100} = 80 \, \text{ml} \]

### Step 2: Calculate the volume of nitrogen in the air
The remaining volume in the air after accounting for oxygen will be nitrogen. Since air is primarily composed of nitrogen and oxygen, we can find the volume of nitrogen by subtracting the volume of oxygen from the total volume of air.

\[ \text{Volume of Nitrogen} = \text{Total Volume of Air} - \text{Volume of Oxygen} \]
\[ \text{Volume of Nitrogen} = 400 \, \text{ml} - 80 \, \text{ml} = 320 \, \text{ml} \]

### Step 3: Conclusion
The volume of residual nitrogen after the combustion of the gaseous hydrocarbon is 320 ml.

### Final Answer:
The volume of residual nitrogen is **320 ml**.

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