First IE of `5d` seties element are higher than those of `3d` and `4d` series elements. This is due to:

Options

A. bigger size of atoms of `5d` -series elements than `3d` series elements
B. Greater effective nuclear charge is experienced by valence electrons because of the weak shielding of the nuclear by `4f`-electrons in `5d` series.
C. (A) and (B) both
D. None of these

Answer

B

Explanation

The order of shielding effect of various orbital electrons is `sgtpgtdgtf`.Due to the poor shielding effect of `4f-` electrons in `5d-series` elements, there is enhanced increase in effective nuclear charge. As a result of this the valence electrons are tightly bound with the nucleus and thus their removal required higher energy.