Avalanche breakdown in a $PN$ junction diode is due to

The current $I$ in the circuit shown below is: (All diodes are ideal and identical)

Which one of the following represents a forward-biased diode?

The current in the following circuit is:

Find the current through the $1\,\Omega$ resistance in the given circuit.

$A$ $2 \text{ V}$ battery is connected to a diode in forward bias. $A$ voltage of $0.5 \text{ V}$ is dropped across the diode,which is independent of the current flowing through it. $A$ current greater than $10 \text{ mA}$ causes excessive heating and damages the diode. If a current of $5 \text{ mA}$ is required in the diode,what value of series resistance must be connected in the circuit?