Question

how would you explain the lower atomic radius of Ga as compared to Al?​

Answer 1

Answer:

As we go down the p-block groups from period - 3 to period -4 , the d block is also filled with electrons, which means that the next electrons filled in the p-subshell will experience a weaker screening effect of the diffuser D-Block electrons meaning that the nucleus will now strongly be able to attract the valence electrons thus reducing the size of the atom over the effect of Increase of size on moving down the group that is the addition of an extra orbit.

Hope this helps you !