Greenhouse gas is the gas that has the property of absorbing infrared radiation emitted from Earth's surface and reflecting it back to Earth's surface, thus contributing to the greenhouse effect.
Carbon dioxide, methane, nitrous oxide, and water vapour are the most important greenhouse gases.
Argon is not a greenhouse gas because it allows the sunlight rays to pass through them which further does not promote the rise in temperature of the earth.
Option B is correct.