Which is the primary constitutional unit for diode and transistor?

Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$: $A$ diode under reverse-biased condition provides very small current which is nearly independent of voltage until a critical limit at which the current increases drastically.
Reason $R$: Below the critical voltage limit,only majority charge carriers flow which increases drastically above critical voltage.

Assertion: The value of current through the $p-n$ junction in the given figure will be $10\, mA$.
Reason: In the above figure,the $p-$side is at a higher potential than the $n-$side.

Which one of the diodes given below is reverse biased?

In the circuit shown for the given input voltage $V_i$, the maximum output voltage $V_0$ is

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