Thallous chloride is more stable than thallic chloride because of

Thallous chloride (TlCl) is more stable than thallic chloride (TlCl₃) due to the inert pair effect. Thallium (Tl) belongs to group 13 of the periodic table, which means it has three valence electrons. In thallic chloride, all three valence electrons of Tl are involved in bonding with chlorine, resulting in the formation of TlCl₃. However, in thallous chloride, only one of the valence electrons of Tl is involved in bonding with chlorine, and the other two electrons remain paired and inert.

This inert pair effect arises from the poor shielding of the valence electrons in the inner shells of heavy elements like thallium. As a result, the outermost electrons experience a stronger effective nuclear charge, making them less easily available for bonding. Therefore, Tl⁺ ion in thallous chloride is more stable and less likely to form a covalent bond with chlorine compared to Tl³⁺ ion in thallic chloride.