Which of the following diodes is reverse biased?

For an ideal diode,in forward and reverse biased condition the resistance is respectively

$A$ diode operates at a constant potential drop of $0.5\, V$ for all currents and has a maximum power rating of $100\, mW$. If the source voltage is $1.5\, V$,what resistance must be connected in series with the diode so that the current in the circuit is at its maximum safe value? (in $\Omega$)

The given circuit has two ideal diodes connected as shown in the figure. The current flowing through the resistance $R_1$ will be.....$ A$

In the following circuit of $PN$ junction diodes $D_1, D_2$ and $D_3$ are ideal,then the current $i$ is:

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