How can you explain the higher stability of $BCl_3$ as compared to $TlCl_3$?

(N/A) Boron and thallium belong to group $13$ of the periodic table.
In this group,the $+1$ oxidation state becomes more stable as we move down the group due to the inert pair effect.
$BCl_3$ is more stable than $TlCl_3$ because the $+3$ oxidation state of $B$ is more stable than the $+3$ oxidation state of $Tl$.
In $Tl$,the $+3$ oxidation state is highly oxidising and it tends to revert to the more stable $+1$ oxidation state.