What is dark current in photodiode?

Two $p$ - $n$ photodiodes are fabricated from semiconductors with band gap of $2.8\mathrm{eV}$ and $2.6\mathrm{eV},$ respectively.

Choose the correct statement from the following.

How can we reduce dark current in photodiode?

Represent the union of two sets by Venn diagram for each of the following.

$X=\{x | x$ is a prime number between $80$ and $100\}$

$Y=\{y | y$ is an odd number between $90$ and $100\}$