CBSE Class 10 Answered

Chlorophyll-a is the primary photosynthetic pigment and chlorophyll-b is the accessory pigment that collects the solar energy to pass on to chlorophyll-a.

Chlorophyll a absorbs well at a wavelength of about 450 nm but its primary absorption is at 675nm in the long red wavelengths.
Chlorophyll b absorbs most effectively at blue 470 but also with shorter peaks at 430 and 640nm.
Chl-b differs from chl-a by its 7-formyl group.

All plants, algae, and cyanobacteria which photosynthesize contain chlorophyll a. Chlorophyll b, occurs only in green algae and in the plants.