Select the correct statement regarding the color of photosynthetic pigments:
$(1)$ Chlorophyll $a$ appears yellow-orange in color.

What is the correct chemical formula for $\beta$-carotene?

Which of the following is a proteinaceous and water-soluble photosynthetic pigment?

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 of the following compounds lacks iron?

The functional unit of the chloroplast is ......