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 `O_2` used is:

Options

A. 70 ml
B. 75 ml
C. 80 ml
D. 85 ml

Explanation

To find the volume of \( O_2 \) used in the combustion of a gaseous hydrocarbon, we can follow these steps:

### Step 1: Understand the given data
- Volume of gaseous hydrocarbon = 20 ml
- Volume of air required for combustion = 400 ml
- Percentage of \( O_2 \) in air = 20%
- Volume of air after combustion (cooling) = 380 ml

### Step 2: Calculate the volume of \( O_2 \) in the air
Since air contains 20% \( O_2 \), we can calculate the volume of \( O_2 \) present in 400 ml of air.

\[ \text{Volume of } O_2 = \frac{20}{100} \times 400 \text{ ml} \]

Calculating this gives:

\[ \text{Volume of } O_2 = 80 \text{ ml} \]

### Step 3: Conclusion
The volume of \( O_2 \) used for the complete combustion of the gaseous hydrocarbon is 80 ml.

### Final Answer
The volume of \( O_2 \) used is **80 ml**.

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