The correct option is D Mitosis
Introduction to gamete
Gametes are haploid cells that are produced in the respective male or female gonads.
In sexual reproduction, male and female gametes fuse to form a diploid zygote by the process of fertilisation.
Mitosis
In haploid (n) plants gametophytes undergo mitotic division to produce the haploid gametes.
This is because mitosis helps in the production of daughter cells having the same number of chromosomes as the parent cell.
The haploid gametes fuse to form zygote (2n) which develops into a sporophyte.
Final answer
(b) Mitosis