The phase of photosynthesis in which sugar is synthesized by reducing CO₂ is also called the dark reaction because:

Explanation

The dark reaction, also known as the Calvin cycle, is called so because it does not require light directly to carry out its chemical processes. During this phase, carbon dioxide is reduced to form sugars using the energy stored in ATP and the reducing power of NADPH, both of which are produced in the light-dependent reactions. Although it relies on the products of light reactions, the chemical steps of carbon fixation, reduction, and regeneration can proceed without light, which is why this phase is referred to as the dark reaction.