21) B

1 – Correct
Gametes are the only cells in animals produced by meiosis.

2 – Correct
Mitosis is basically replication of cells.

3 – Wrong
Meiosis results in 4 haploid nuclei.

4 – Wrong
Mitosis result in 2 identical diploid nuclei.

5 – Correct
Mitosis occurs during asexual reproduction. An identical individual(clone) is formed during asexual reproduction.

1, 2 and 5 are correct statements. So, B is correct.