In the carbon cycle, carbon dioxide in the air may be replenished by

In the carbon cycle, carbon dioxide in the air may be replenished by different processes. The question is asking which process is responsible for replenishing carbon dioxide in the air.

The correct answer is Option A: respiration.

Respiration is a process that occurs in living organisms, including plants and animals. During respiration, organisms take in oxygen and release carbon dioxide as a waste product. This carbon dioxide is then released into the air, contributing to the carbon dioxide levels in the atmosphere.

Transpiration, which is Option B, is the process by which plants release water vapor into the air through small openings in their leaves called stomata. While transpiration does release some water vapor into the air, it does not directly replenish carbon dioxide in the atmosphere.

Lightning, which is Option C, can produce nitrogen oxides that can react with oxygen to form nitrogen dioxide, but it does not directly replenish carbon dioxide in the air.

Denitrification, which is Option D, is a process in the nitrogen cycle where bacteria convert nitrates back into nitrogen gas. It does not directly replenish carbon dioxide in the air.

So, the correct answer is Option A: respiration, as it is the process that contributes to the replenishment of carbon dioxide in the air during the carbon cycle.