What is the current in the following junction diode circuit?

$A$ diode having a potential difference of $0.5\, V$ across its junction,which does not depend on the current,is connected in series with a resistance of $20\, \Omega$ across a source. If $0.1\, A$ passes through the resistance,then what is the voltage of the source (in $, V$)?

In the figure shown, if the diode forward voltage drop is $0.2 \, V$, the voltage difference between $A$ and $B$ is (in $V$)

If the $p-n$ junction diode is unbiased,

Statement $I :$ When a $Si$ sample is doped with Boron,it becomes $P$-type and when doped by Arsenic it becomes $N$-type semiconductor such that $P$-type has excess holes and $N$-type has excess electrons.
Statement $II$ : When such $P$-type and $N$-type semiconductors are fused to make a junction,a current will automatically flow which can be detected with an externally connected ammeter.
In the light of above statements,choose the most appropriate answer from the options given below.

The $V-I$ characteristic of a silicon diode is shown in the Figure. Calculate the resistance of the diode at $(a) \; I_{D} = 15 \, mA$ and $(b) \; V_{D} = -10 \, V$.