Under the same conditions the rate of diffusion of two gases are in the ratio 1:4 the ratio of their vapour densities is

The phenomenon of diffusion of a gas can be defined as the tendency of a gas to spread uniformly throughout the space available to it.

The relation between its density and the rate of diffusion of a gas can be represented by Graham’s law which states that "The rate of diffusion of a gas is inversely proportional to the square root of its density under given conditions of temperature and pressure."

It can be mathematically expressed as

If r₁ & r₂ are rates of diffusion with densities d₁ & d₂ the above equation becomes,

So ratio of diffusion of two gases under same conditions are 1:4 , so the ratio of their vapour density under same conditions will be 4:1
Hope it is clear
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