The Total solution for NCERT class 6-12
BCl3 is quite stable. Because there is absence ofd- and f-electrons in boron three valence electrons (2s2 2px1) are there for bonding with chlorine atom. In Tlthe valence s-electron (6s2) are experiencing maximum inert pair effect.Thus, only 6p1 electron is available for bonding.Therefore, BCl3 is stable but TlCl3 is comparatively unstable.