Question

Arrange the following in increasing order of first ionization enthalpy:

Al, Ga, In, Tl, B 

(1) Tl < In < Ga < Al < B 

(2) In < Al < Ga < Tl < B 

(3) In < Ga < Al < B < Tl 

(4) B < Al < Ga < In < Tl

Answer 1

Correct option is (2) In < Al < Ga < Tl < B 

Due to poor shielding by electrons in d-subshell of Ga and f-subshell of Tl, their ionization energy increases than the expected value. 

So, correct order of IE-

In < Al < Ga < Tl < B