Why do members of Phaeophyceae vary in colour from olive green to various shades of brown?

Why do light rays bend when they enter from one optical medium to another?

Leaves of the same plant as well as the leaves of different plants show different shades of green. Name the pigments reponsible for the colour of leaves.

Why do we place handles at maximum possible distance from the hinges in a door?

Why is the colour of a leaf kept in the dark frequently yellow, or pale green? Which pigments do you think is more stable?

A blackish brown coloured solid 'A' when fused with alkali metal hydroxides in presence of air, produces a dark green coloured compound 'B' which on electrolytic oxidation in alkaline medium gives a dark purple coloured compound 'C' Identify A, B and C and write the reactions involved.

Look at leaves of the same plant on the shady side and compare it with the leaves on the sunny side. Or, compare the potted plants kept in the sunlight with those in the shade. Which of them has leaves that are darker green? Why?