Question

Why the oxidation state of -3 of group 13 elements decrease down the group

Answer 1

Dear student

​​​​​Top ​​elements in 13 group, generally show +3 oxidation state as they have a valency of 5 and need to lose 3 more electrons to attain stability.
But as we move down the group, the +3 oxidation state decreases and stability of +1 oxidation state increases due to inert pair effect.
The inert pair effect is defined as the tendency of electrons in the outermost atomic s orbital to remain unionized in compounds of post-transition metals.

Hence, group 13 elements are not able to lose electron form 2s orbitals and +1 O.S become more stable for heavier elements ( elements down the group)

Regards