A single set of chromosomes is found in

(i) Secondary oocyte

(ii) Spermatogonium

(iii) Primary spermatocyte 

(iv) Secondary Spermatocyte

(v) Spermatid

i. Secondary oocyte - Haploid or contains a single set of chromosome

ii. Spermatogonium - Diploid cells, each contains 46 chromosome (23 pairs) 

iii. Primary spermatocyte -  Diploid because they produced by mitosis and have 46 chromosome.

iv. Secondary spermatocyte - Haploid because each primary spermatocytes goes through the first meiotic division to produce two secondary spermatocytes each with 23 chromosome. 

v. Spermatid - Haploid male gamete which results from division of secondary spermatocyte. 

Hence, germinal cell, secondary spermatocyte and spermatid contains only one set of chromosome or haploid in nature.