The second stage of photosynthesis, in which carbon dioxide is reduced to carbohydrate and which occurs whether light is present or not, is called:

Explanation

The correct answer is the light-independent reaction, also known as the Calvin cycle. This phase occurs in the stroma of chloroplasts and uses ATP and NADPH produced during the light-dependent reactions to fix carbon dioxide and produce glucose. It is termed 'light-independent' because it does not require light directly, although it relies on the products of the light-dependent reactions.The other options refer to processes that are part of the light-dependent reactions, which occur in the thylakoid membranes and require light. The 'light-dependent reaction' is a term used to describe the same phase where light energy is converted into chemical energy. 'Synthesis of ATP and NADPH2' is a process that happens during these light-dependent reactions, not the Calvin cycle.