Final answer:
Water vapor is a strong greenhouse gas. It is more effective at trapping heat in the atmosphere than other gases like nitrogen or oxygen.
Step-by-step explanation:
The question asks which of the following options is a strong greenhouse gas. The correct answer is 2. water vapor. Greenhouse gases are gases in Earth's atmosphere that trap heat. They let sunlight pass through the atmosphere, but they prevent the warmth that the sunlight brings from leaving the atmosphere. Among the options provided, nitrogen and oxygen are not strong greenhouse gases. However, water vapor is a potent greenhouse gas because it absorbs more heat in the atmosphere than some other gases like carbon dioxide. Thus, water vapor significantly contributes to the warming of the Earth.
Learn more about Greenhouse Gases