Solution

Chlorophyll (mainly chlorophyll a, with chlorophyll b and accessory pigments) present in the thylakoids absorbs light energy, mainly in the blue and red regions.
This energy excites electrons in the reaction centre and drives the light reaction.
Water is split to provide electrons, $O_2$ is a by-product, and RuBP is the $CO_2$ acceptor; none of these absorbs light for photosynthesis.
So chlorophyll absorbs light energy for photosynthesis.

Concept Chlorophyll traps light

Photosynthetic Pigments in past papers

3 questions from this chapter have appeared across 3 exam years.