All gases diffuse rapidly but different rates. for example carbon dioxide diffuses slower than oxygen gas and hydrogen gas. the rate of diffusion of each gas is dependent on its
a) bond type
b) solubility
c) molecular mass
d) electronegativity

Gas is a state of matter is always in motion. It has no fixed shape but will take the shape of the space provided. Gas also doesn't have a fixed volume but will fill the space available. The movement of the gas depends on the molecular mass. Diffusion is movement of molecules across its concentration gradient. Carbon dioxide molecular mass is higher than oxygen and hydrogen so that is why it diffuses slower. 

The answer is d.potassium