Depletion region in an unbiased semiconductor diode is a region consisting of

Which of the following represents a reverse-biased diode?

In the given figure,each diode has a forward bias resistance of $30\, \Omega$ and infinite resistance in reverse bias. The current ${I}_{1}$ will be $....\,A$.

When the $P$ end of a $P-N$ junction is connected to the negative terminal of the battery and the $N$ end to the positive terminal of the battery,then the $P-N$ junction behaves like:

On adjusting the $P-N$ junction diode in forward biased,what happens to the depletion layer and the resistance?

The voltage-current characteristic of a diode during forward bias is given by $I = 7.8 \times 10^{-5} e^{6.5 V_D}$, where $I$ is the current in $mA$ and $V_D$ is the diode voltage in $V$. Find the dynamic resistance of the diode in $\Omega$, when the current is $4 \ mA$.