Q. Which member of group 13 does not exhibit the group valency in its compounds?

 2061  201 NTA AbhyasNTA Abhyas 2020Classification of Elements and Periodicity in Properties Report Error

Solution:

The usual oxidation state of group 13 is +3, but due to inert pair effect, both the s-electrons of the outer shell remains paired, due to energy considerations in case of thallium. Consequently, Tl show +1 oxidation state.