### Q.12:- From a certain apparatus, the diffusion rate of hydrogen has an average value of 28.7 cm^{3} s^{–1}. The diffusion of another gas under the same conditions is measured to have an average rate of 7.2 cm^{3} s^{–1}. Identify the gas.

[Hint: Use Graham’s law of diffusion: R_{1}/R_{2} = (M_{2}/M_{1})^{1/2}, where R_{1}, R_{2} are diffusion rates of gases 1 and 2, and M_{1} and M_{2} their respective molecular masses. The law is a simple consequence of kinetic theory.]

**Answer:-**

Rate of diffusion of hydrogen, *R*_{1 }= 28.7 cm^{3} s^{–1}

Rate of diffusion of another gas, *R*_{2} = 7.2 cm^{3} s^{–1}

According to Graham’s Law of diffusion, we have:

32 g is the molecular mass of oxygen. Hence, the unknown gas is oxygen.