Which of the following will have the slowest rate of diffusion at a given temperature?

CI2

H2

He

Ne

Chlorine gas (Cl₂)

Explanation: According to the Graham's law of diffusion, the diffusion rate of a gas is inversely proportional to the square root of its density or molar mass. Therefore, a lighter gas will diffuse faster at a given temperature compared to a heavy gas. Consequently, the heavier a gas is then the denser it is and the slower it diffuses at a given temperature and vice versa.

In this case we are given gases, CI₂

, H₂, He and Ne.

We are required to identify the gas that will diffuse at the slowest rate. In other words we are required to determine the heaviest gas.

Looking at the molar mass of the gases given;

Cl₂ - 70.91 g/mol

H₂ - 2.02 g/mol

He - 4.00 g/mol

Ne - 20.18 g/mol

Therefore, chlorine gas is the heaviest and thus will diffuse at the slowest rate among the choices given.