The egg should be candled on . . . . . . . . day of incubation.

Solution(By Examveda Team)

The egg should be candled on 3^rd day of incubation.
Incubated eggs are candled to determine whether they are fertile and, if fertile, to check the growth and development of the embryo. White eggs should be tested for fertility on the third day. Brown shelled eggs on the fifth or sixth day because it is difficult to see the embryo clearly before this time.
Eggs may be candled after 3 days of incubation and every few days thereafter. For best results you should candle eggs in a darkened room or dimly lit conditions. The candler should be held right against the shell at the larger end of the egg where the air sac is located.