Explanation:

The rate of diffusion of a gas is inversely proportional to the square root of its molar mass (Graham's Law of Diffusion).

* Molar mass of AsH3: 77.94 g/mol

* Molar mass of HCN: 27.03 g/mol

Since HCN has a lower molar mass than AsH3, it will diffuse faster.

Therefore, HCN will diffuse faster than AsH3.