Explanation:

- Option 1: Water vapour

- Water vapor is a significant greenhouse gas.

- It absorbs heat and increases Earth's temperature through the greenhouse effect.

- Option 2: Oxygen

- Oxygen is not a greenhouse gas.

- It does not trap heat in the atmosphere.

- Oxygen mainly supports combustion and respiration processes.

- Option 3: Carbon dioxide

- Carbon dioxide is one of the key greenhouse gases.

- Human activities like burning fossil fuels increase its levels.

- Option 4: Methane

- Methane is a potent greenhouse gas, albeit present in smaller quantities.

- It has a much higher heat-trapping ability than carbon dioxide.

- Correct Answer: Option 2 - Oxygen