• # question_answer 62)   The reason for small radius of $Ga$compared to Al is.......... (a) poor screening effect of d- and f-orbitals       (b) increase in nuclear charge (c) presence of higher orbitals                                   (d) high atomic number

(a, b) Both Al and $Ga$have nearly the same value of ionisation enthalpy inspite of the fact that $Ga$should have much lower value. This is due to the fact that screening effect of ten d-electrons present in the penultimate shell is poor and the outer electron is thus held firmly.