Rate of diffusion of a gas is _________

Question

$\begin{array}{1 1} \text{(a)directly proportional to its density} \\ \text{ (b) directly proportional to its molecular mass} \\ \text{(c) directly proportional to the square root of its molecular mass} \\ \text{ (d) inversely proportional to the square root of its molecular mass} \end{array}$