Point out the odd one from the given options.

Pollen grain

The correct answer is Option (4) -Pollen grain

The options (1), (2), and (3) - Nucellus, Embryo sac, and Micropyle - are all parts or structures associated with the female reproductive system of a flower.

Nucellus refers to the central part of the ovule, which houses the megasporangium and eventually develops into the seed after fertilization.

Embryo sac is the female gametophyte, which is formed from a single functional megaspore and contains the egg cell and other cells necessary for fertilization and embryonic development.

Micropyle is a small opening or pore in the ovule, which serves as a passage for the entry of pollen tube during fertilization.

On the other hand, a pollen grain is a male reproductive structure produced by the anther of a flower. It contains the male gametes. Pollen grains are released from the anther and are responsible for the transfer of male gametes to the stigma for fertilization.

Therefore, the odd one out is (4) Pollen grain, as it is a male reproductive structure, while the other options are associated with the female reproductive system of a flower.