What are the three cells present in a pollen grain when it is shed at…

The correct answer is Option (1) → 1 vegetative cell, 2 male gametes.

A mature pollen grain at first has two cells: a large vegetative cell and a small generative cell. In some species the generative cell divides by mitosis before the pollen is shed and forms two male gametes. Such pollen is shed at the 3-celled stage: one vegetative cell and two male gametes.

Option (1) 1 vegetative cell, 2 male gametes. — Correct. At the 3-celled stage the pollen grain has one vegetative cell and two male gametes.

Option (2) 1 vegetative cell, 1 generative cell, 1 male gamete. — Incorrect. A generative cell together with a male gamete is not possible. The generative cell divides to give both male gametes, so once gametes are formed there is no generative cell left.

Option (3) 2 generative cells, 1 male gamete. — Incorrect. A pollen grain has only one generative cell, and it is not present at the 3-celled stage. The vegetative cell is also missing from this option.

Option (4) 1 generative cell, 2 male gametes. — Incorrect. This leaves out the vegetative cell, which is present at both stages, and keeps the generative cell, which has already divided.

NCERT Extract:
Stamen, Microsporangium and Pollen Grain – “… In over 60 per cent of angiosperms, pollen grains are shed at this 2-celled stage. In the remaining species, the generative cell divides mitotically to give rise to the two male gametes before pollen grains are shed (3-celled stage).”
Summary – “… Pollen grains may have two cells (a vegetative cell and generative cell) or three cells (a vegetative cell and two male gametes) at the time of shedding.”