The gas that could be identified as gas B is helium(He).
We know that the rate of diffusion of a gas is inversely proportional to the square root of the molar mass of the gas. If we then have two masses of gas then we can write;
R1/R2 = √M2/M1
Given that;
R1 = rate of diffusion of gas 1
R2 = rate of diffusion of gas 2
M2 = molar mass of gas 2
M1 = molar mass of gas 1
We are told that Gas 2 diffuses 3.16 times faster than gas 1. We now know that;
1/3.16 = √M2/40
(1/3.16)^2 = M2/40
1/9.99= M2/40
40 = 9.99 M2
M2 = 40/9.99
M2 = 4
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