Final answer:
The effusion rate of a gas is proportional to the square root of its molar mass.
Step-by-step explanation:
The statement that the effusion rate of a gas is proportional to the square root of its molar mass is true. This relationship is known as Graham's law. According to Graham's law, if two gases A and B are at the same temperature and pressure, the ratio of their effusion rates is inversely proportional to the ratio of the square roots of the masses of their particles.