2. The discontinuity in ionization enthalpy values of group 13 elements in the periodic table is due to a) irregular variation in ionic radii b) irregular variation in electronegativity c) poor shielding effect of ‘p’ and ‘d’ electrons d) poor shielding effect of ‘d’ and ‘f’ electrons

The ionization enthalpy values as expectedfrom the general trends do not decreasesmoothly down the group.
The decrease fromB to Al is associated with an increase in size. Theobserved discontinuity in the ionizationenthalpy values between Al and Ga, andbetween In and Tl are due to the inability of d- andf-electrons, which have low screening effect, tocompensate the increase in nuclear charge.