Question

carbon dioxide is a greenhouse gas because too much of it can trap _______ in the atmosphere.
heat
nitrogen gas
water

Explanation:

Greenhouse gases like carbon - dioxide trap heat in the atmosphere. They allow sunlight to enter but prevent the heat radiated from the Earth's surface from escaping back into space, thus warming the planet. Nitrogen gas is a major component of the atmosphere but is not a greenhouse gas and water vapor is also a greenhouse gas but not the answer here as carbon - dioxide traps heat.

Answer:

Heat