In general, the first ionisation energy decreases in a regular way on descending the main groups. A

Question

In general, the first ionisation energy decreases in a regular way on descending the main groups. A departure from this trend is observed in Group 13 as follows : \ Gallium has higher ionisation energy in comparison to Al because\ A. gallium is harder than aluminium\ B. gallium is preceded by ten transition elements, where $3 d$ shell is being filled which makes Ga larger than it would be\ C. gallium is preceded by ten transition elements, where $3 d$ shell is being filled which makes Ga smaller than it would be\ D. effective nuclear charge for Ga is much higher than Al.\

Professor PC Thomas Classes · Answer

(c) : Ineffective shielding causes decrease in size.