The atomic weight of helium is 4 times that of hydrogen. Its diffusion rate as compared to hydrogen will be __________ times.

ANS:C - 2

The diffusion rate of a gas is inversely proportional to the square root of its molar mass. This relationship is described by Graham's law of diffusion. If the atomic weight of helium (𝐻𝑒He) is 4 times that of hydrogen (𝐻2H2​), then the molar mass of helium (𝑀𝐻𝑒MHe​) is also 4 times that of hydrogen (𝑀𝐻MH​). According to Graham's law of diffusion, the ratio of diffusion rates of two gases is given by: Rate of diffusion of gas A:Rate of diffusion of gas B=𝑀𝐵𝑀𝐴Rate of diffusion of gas A:Rate of diffusion of gas B=MA​MB​​​ Substituting the given molar mass values: Rate of diffusion of helium:Rate of diffusion of hydrogen=𝑀𝐻2𝑀𝐻𝑒=𝑀𝐻𝑀𝐻𝑒=14=12Rate of diffusion of helium:Rate of diffusion of hydrogen=MHe​MH2​​​​=MHe​MH​​​=41​​=21​ Therefore, the diffusion rate of helium as compared to hydrogen will be 1221​​ times.