`80` mL of ammonia gas effuse out form a vessel in `8` minute at `5^(@)C` and `500 mm` Hg pressure. How long will `40` mL of a certain gas with molecular mass 68 take to effuse out form the same vessel at the same temperature and pressure ?

Explanation

To solve the problem, we will use Graham's law of effusion, which states that the rate of effusion of a gas is inversely proportional to the square root of its molar mass.

### Step-by-Step Solution:

1. **Identify Given Data:**
- Volume of ammonia (NH₃) = 80 mL
- Time taken for ammonia to effuse = 8 minutes
- Volume of the unknown gas = 40 mL
...