When a p - n junction is reverse-biased, the current is nearly...

In a $p$-$n$ junction diode, the net current is the difference between the diffusion current and the drift current.

The drift current is due to the flow of minority charge carriers and is relatively independent of the applied bias voltage. It is equal to the reverse saturation current.

Given that the reverse-biased current is $25 \mu\text{A}$, the drift current is $I_{\text{drift}} = 25 \mu\text{A}$.

When the diode is unbiased, the net current through the junction is zero.

$I_{\text{net}} = I_{\text{diffusion}} - I_{\text{drift}} = 0$

$\Rightarrow I_{\text{diffusion}} = I_{\text{drift}} = 25 \mu\text{A}$