In a forward-biased $P-N$ junction diode,how does the potential barrier behave?

In the circuit shown, assume the diode to be ideal. When $V_{i}$ increases from $2 \ V$ to $6 \ V$, the change in the current is (in $mA$):

When a $PN$ junction diode is reverse biased,

Which of the following statements concerning the depletion zone of an unbiased $PN$ junction is (are) true?
$(A)$ The width of the zone is independent of the densities of the dopants (impurities).
$(B)$ The width of the zone is dependent on the densities of the dopants.
$(C)$ The electric field in the zone is produced by the ionized dopant atoms.
$(D)$ The electric field in the zone is provided by the electrons in the conduction band and the holes in the valence band.

In the given circuit,the current is $0.1 \ A$. The resistance of the $P-N$ junction is .... $\Omega$.

The depletion layer in the $P-N$ junction region is caused by