The pollen tube enters the embryo sac through:

The correct answer is Option (4) → micropylar end

Option (4) micropylar end — Correct. The pollen tube must reach one of the synergids. The two synergids and the egg form the egg apparatus, which lies at the micropylar end of the embryo sac. So the tube enters the embryo sac at its micropylar end.

NCERT Extract:
Pollination – “… You would recall that in some plants, pollen grains are shed at two-celled condition (a vegetative cell and a generative cell). In such plants, the generative cell divides and forms the two male gametes during the growth of pollen tube in the stigma. In plants which shed pollen in the three-celled condition, pollen tubes carry the two male gametes from the beginning. Pollen tube, after reaching the ovary, enters the ovule through the micropyle and then enters one of the synergids through the filiform apparatus (Figure 1.12d, e).”
The Pistil, Megasporangium (ovule) and Embryo Sac – “… There is a characteristic distribution of the cells within the embryo sac. Three cells are grouped together at the micropylar end and constitute the egg apparatus. The egg apparatus, in turn, consists of two synergids and one egg cell.”