In a $p-n$ junction diode not connected to any circuit:

In which of the following figures is the $p-n$ junction diode reverse biased?

Which of the following is correct with respect to the following statements? Due to diffusion of electrons from $n$ to $p$-side:
$I$. electrons are accumulated in the depletion region.
$II$. electron drift current is from $p$-side to $n$-side.
$III$. an ionised donor is left in the $n$-region.
$IV$. electrons of $n$-side come to $p$-side and electron-hole combination takes place in $p$-side.
Select the correct option from the following.

The forward biased diode connection is:

For the circuit shown in the figure,$V_{AB} = $ ....... $V$.

Consider a circuit consisting of a capacitor $(20 \mu\text{F})$,a resistor $(100 \Omega)$,and two identical diodes as shown in the figure. The resistance of each diode under forward biasing condition is $10 \Omega$. The time constant of the circuit is $\alpha \times 10^{-3} \text{ s}$. The value of $\alpha$ is . . . . . . .