• # question_answer 32) How would you explain the lower atomic radius of $Ga$as compared to Al?

Due to poor shielding of the valence electrons in $Ga$ by the inner d-electrons, the effective nuclear charge is high in comparison to Al. As a result, the attractive force with which the valence electrons are attracted is high. This brings contraction in size and hence, atomic size of $Ga$ is lower in comparison to Al.