What is the number of pigment molecules in a quantasome?

The role of phycobilins in photosynthesis is to

Which of the following pigments is soluble in water?

Chlorophyll $a$ is absent in which of the following photosynthetic organisms?

In the figure given below,the black line (upper) indicates the action spectrum for photosynthesis and the lighter line (lower) indicates the absorption spectrum of chlorophyll-$a$. Answer the following:
$(a)$ What does the action spectrum indicate? How can we plot an action spectrum? Explain with an example.
$(b)$ How can we derive an absorption spectrum for any substance?
$(c)$ If chlorophyll-$a$ is responsible for the light reaction of photosynthesis,why do the action spectrum and absorption spectrum not overlap?

Which light of the visible spectrum is absorbed by carotenoids in higher plants from solar radiation?