Ans.
Chlorophyll b is a green colored, accessory photosynthetic pigment that helps in the process of photosynthesis by collecting enegry. It traps solar energy and transfers it to the chlorophyll a.
Chlorophyll b absorbs red and blue light of electromagnetic spectrum, which ranges from 650-680 and 450-480 nano meter. The light primarily absorbed by the chlorophyll b is blue light.
Thus, the correct answer is 'blue light.'