Question

which have greater size gallium or indium and why?​

Answer 1

Indium has the larger size from the both.

Answer 2

Ga and In are in different periods, although they're in the same group.

Ga is in Period 4, thus it has 4 electronic shells. In is in Period 5, this it has 5 electronic shells. Thus, In has a higher shielding effect than Ga, and its metallic radius will thus be larger because the distance between the nucleus and the valence electrons is also larger.