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

Answer:

  (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.