Which of the following options correctly describes the embryo sac in…

The correct answer is Option (3) → The embryo sac is the female gametophyte

The ovule is the megasporangium of a flowering plant. Inside it, the megaspore mother cell divides by meiosis and forms four megaspores. Usually only one of them is functional. This functional megaspore grows into the embryo sac, which is the female gametophyte. When mature, the embryo sac has seven cells, and one of them is the egg.

Option (1) The embryo sac is the female gamete — Incorrect. The female gamete is the egg cell. It is only one of the seven cells of the embryo sac, so the embryo sac as a whole is not the gamete.

Option (2) The embryo sac is the megasporangium — Incorrect. The megasporangium is the ovule itself. It holds the integuments, the nucellus and the embryo sac, so the embryo sac is only a part of it.

Option (3) The embryo sac is the female gametophyte — Correct. The embryo sac develops from the functional megaspore. It is the haploid generation that bears the egg, which makes it the female gametophyte.

Option (4) The embryo sac is the ovule — Incorrect. The ovule is the whole structure attached to the placenta by its stalk. The embryo sac lies inside its nucellus, so the two are not the same.

NCERT Extract:
The Pistil, Megasporangium (Ovule) and Embryo Sac – “… Enclosed within the integuments is a mass of cells called the nucellus. Cells of the nucellus have abundant reserve food materials. Located in the nucellus is the embryo sac or female gametophyte. An ovule generally has a single embryo sac formed from a megaspore.”
The Pistil, Megasporangium (Ovule) and Embryo Sac – “… Female gametophyte : In a majority of flowering plants, one of the megaspores is functional while the other three degenerate. Only the functional megaspore develops into the female gametophyte (embryo sac).”