At $0 K$, an intrinsic semiconductor behaves as a-

In the case of forward biasing of a $p-n$ junction diode, which one of the following figure correctly depicts the direction of conventional current ?

The contribution in the total current flowing through a semiconductor due to electrons and holes are $\frac{3}{4}$ and $\frac{1}{4}$ respectively. If the drift velocity of electron is $\frac{5}{2}$ times that of holes at this temperature, then the ratio of concentration of electrons and holes is