At 400 K, the root mean square (rms) speed of gas X -(molecular mass = 40) is equal the most probable speed of gas Y at 60K. The molecular mass of the gas Y is

Explanation

`(sqrt((3RT)/M))_X=(sqrt((2RT)/M))_Y`
`(sqrt((3R400)/40))=(sqrt((2R60)/M))`
`sqrt30=sqrt((4xx30)/M)`
M = 4