The right answer is A. light reaction.
Hill's reaction is an oxidation-reduction reaction taking place during photosynthesis, experimentally demonstrated by the British biochemist Robert Hill in 1937 and 1939. He showed that the photosynthesis reaction can be reduced to two reactions forming a single reaction redox system.
Hill's reaction is represented by the following equation:
2 H2O + 2A+ (light, chloroplasts) → 2 AH2 + O2.
