Helium diffuses 4 times faster than an unknown gas under similar conditions. Find the vapour density of unknown gas.

Explanation

To solve the problem of finding the vapor density of an unknown gas that diffuses at a rate 4 times slower than helium, we can follow these steps:

### Step 1: Understand the relationship between diffusion rates and molecular weights
The rate of diffusion of a gas is inversely proportional to the square root of its molecular weight. This relationship can be expressed mathematically as:
\[ \text{Rate} \propto \frac{1}{\sqrt{M}} \]
where \( M \) is the molecular weight of the gas.
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