What is the use of diode?

Draw circuit diagram for a $\mathrm{P}-\mathrm{N}$ junction to obtain reverse bias characteristic curves. Explain the phenomenon of reverse breakdown for a $\mathrm{P}-\mathrm{N}$ junction in reverse bias state by following process-

$\left(\mathrm{i}\right)$ Avalanche breakdown

An ideal diode $D$ and a resistance $R$ are connected in series with an alternating voltage source $V\left(t\right)=V_0\sin \omega t$. If the root-mean-square value of the voltage $\left(V_x\right)$ is measured at the point $X$, as shown, the result will be

In the following circuit diagram, the current through the battery is

In the following figure, identify the diodes which are reverse biased

(A)

(B)

(C)

(D)