Which of the following must be zero in an unbiased PN junction diode?

In an unbiased p-n junction, there is no applied emf across the diode and hence no current flows due to minority or majority carriers. The net current is zero because the diffusion current of majority carriers (electrons from the n-side and holes from the p-side) is exactly balanced by the drift current of minority carriers (holes from the n-side and electrons from the p-side). Therefore, the total current is zero.