The function of germ pore in a pollen grain is:

The correct answer is Option (2) → To form the pollen tube

The tough outer wall of the pollen grain, the exine, is made of sporopollenin. It has small gaps called germ pores, where sporopollenin is absent. When the pollen grain germinates on the stigma, the pollen tube grows out through one of the germ pores.

Option (1) To protect the pollen grain — Incorrect. Protection is the job of the exine; the germ pores are the gaps in it.

Option (2) To form the pollen tube — Correct. The exine of the pollen grain has prominent apertures called germ pores, where sporopollenin is absent. During germination, the pollen tube comes out through one of the germ pores.

Option (3) To divide the cells of pollen grain — Incorrect. The cells inside divide by mitosis; the germ pores play no part in it.

Option (4) To store the food — Incorrect. Food is kept in the cytoplasm of the pollen grain, not in the pores.

NCERT Extract:
Pollination – “… As mentioned earlier, following compatible pollination, the pollen grain germinates on the stigma to produce a pollen tube through one of the germ pores (Figure 1.12a). The contents of the pollen grain move into the pollen tube.”