Correct order of strength of $\mathrm{\pi }$ - bond(s) are:

I) ${\mathrm{BO}}_3^{3-}>{\mathrm{CO}}_3^{2-}>{\mathrm{NO}}_3^{-}$

II) ${\mathrm{ClO}}_4^{-}>{\mathrm{SO}}_4^{2-}>{\mathrm{PO}}_4^{3-}$

III) ${\mathrm{BF}}_3>{\mathrm{BCl}}_3>{\mathrm{BBr}}_3$

IV) ${\mathrm{AlCl}}_3>{\mathrm{BCl}}_3$

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 $100\}$

In diborane, the ${\mathrm{H}}_{\mathrm{t}}-\mathrm{B}-{\mathrm{H}}_{\mathrm{t}}$ and ${\mathrm{H}}_{\mathrm{b}}-\mathrm{B}-{\mathrm{H}}_{\mathrm{b}}$ angles are:

(Where, $\mathrm{t}$ denotes terminal and $\mathrm{b}$ denotes bridge)

Which among the following has $3\mathrm{C}-4{\mathrm{e}}^{-}$bond?