The correct option is B Spermatids - 2n
The diploid (2n) oogonia cells of the ovary undergo differentiation and give rise to primary oocyte. Thus primary oocyte is also diploid (2n).
The primary oocyte undergoes meiosis I and gives rise to haploid secondary oocyte (n).
Spermatogonia are diploid cells (2n) that undergo differentiation to give rise to the primary spermatocyte (2n). Primary spermatocyte undergoes meiosis I to form secondary spermatocyte (n). Secondary spermatocyte undergoes meiosis II to form haploid spermatids (n).
Hence option C is incorrect.