The ratio of vapour densities of two gases at the same temperature is 8:9. Compare the rms velocities of their molecules.

Explanation

To solve the problem of comparing the root mean square (RMS) velocities of two gases based on their vapor densities, we can follow these steps:

### Step 1: Understand the relationship between vapor density and molecular mass
The vapor density (D) of a gas is directly proportional to its molecular mass (M). Therefore, we can express this relationship as:
\[ D \propto M \]

### Step 2: Set up the ratio of vapor densities
Given that the ratio of vapor densities of two gases is 8:9, we can write:
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