The molar masses of three gases, a, b, and c, are 4 grams, 16 grams, and 32 grams respectively. which sentence represents the effusion rates of these gases?

This is where something called Graham's Law applies. Grahams law says that the rate of effusion is inversely proportional to the square root of the molar mass of a gas. What that means is that the less the molar mass of a gas is, the less quickly the gas effuses (effusion being the rate at which a gas can travel through a small hole). A great way to think about this is that effusion is thought about as though the gas is traveling through a small hole, so smaller particles would be able to go through it with greater ease than would a large particle. I don't know what particular sentences the question asks for are, but the answer should be that gas A (molar mass 4) has the greatest effusion rate, gas B (molar mass 16) has the second fastest effusion rate, and gas C (molar mass 32) has the slowest effusion rate.