Question

one of the purposes of meiosis is to
produce four zygotes instead of only two (as produced in mitosis)
double the number of chromosomes per gamete
reduce the chromosome number in each resulting cell by half.
increase genetic diversity in the diploid - starting cells
increase the number of embryos per fertilization

Explanation:

Meiosis is a type of cell division. It has two rounds of division. The starting cell is diploid (has two sets of chromosomes). After meiosis, the resulting cells (gametes) are haploid (have one set of chromosomes). So, one of its purposes is to reduce the chromosome number in each resulting cell by half.
Zygotes are formed by fertilization (fusion of gametes), not directly produced by meiosis. Meiosis reduces chromosome number in gametes, not doubles it. Genetic diversity is increased in the haploid - resulting gametes (not diploid - starting cells). And meiosis is about gamete formation, not about increasing the number of embryos per fertilization.

Answer:

reduce the chromosome number in each resulting cell by half.