How can you explain higher stability of `BCl_(3)` as compared to `TlCl_(3)`?

Explanation

In case of boron (B) atom inert pair effect is negligible. This means that all the three valence electrons `(2s^(2)p_(x)^(1))` are available for bonding with chlorine atoms. Therefore, `BCl_(3)` is quite stable. However, in case of thallium (Ti), the valence s-electrons `(6s^(2))` are experiencing maximum inert pair effect. This means that only valence p-electron `(6p^(1))` is available for bonding . Under these clircumstances, TiCl is very much stable while `TiCl_(3)` is comparatively little stable.