Question

$Bi{CI}_5$ doesn't exist.If true enter 1 else 0.

Answer 1

The inertness of s subshell electrons towards the bond formation is called inert pair effect
example:
1) In 13th group, thallium can exhibit +1 and+3 oxidation states but it is stable in +1 oxidation state only due to inert pair effect
2) In 14th group , lead shows both +2 and +4 oxidation states but it is stable in +2 oxidation state due to inert pair effect.
Because of this inert pair effect, Bi forms only +3 oxidation state and forms $BiC{l}_3$ only and due to unstability of +5 oxidation state, $BiC{l}_5$ doesnt exists.