Which structure fuses to form a diploid zygote sexual reproduction

Two haploid cells (sperm and ova).

Explanation:

Sexual reproductions may be defined as a type of reproduction in which two parents are involved in the reproduction. Sexual reproduction brings genetic variation in the offspring.

The male gamete (sperm) and female gamete (ova) fuse together to form a zygote. The gametes are haploid in nature and the product formed by their fusion is diploid in nature, zygote. In case of humans, male gamete are motile and female gamete are non motile.

Thus, the answer is two haploid cells (sperm and ova).

2 haploids fuse together to form a diploid zygote