Which among the following is not the function of testes at puberty?
(i) Formation of germ cells
(ii) Secretion of testosterone
(iii) Development of placenta
(iv) Secretion of estrogen

The correct option is D (iii) and (iv)
Gonads have a dual function, production of hormones and gametes. In the male, testes produce sperms and testosterone.

Placenta develops in females during pregnancy. It has a number of functions, like the production of hormones, nutrition, excretion etc. Estrogen is a female hormone produced by the ovaries (female gonads). Thus, the correct answer is option C.