The first ionisation potential of Al is smaller than that of Mg because:

Options

A. the size of Al is bigger than Mg
B. ionisation enthalpy decrease in a period from left to right
C. it is easier to remove electron from unparied `3 p^(1)` than from paired `3s^(2)`
D. aluminium is a passive metal while magnesium is active metal.

Answer

C

Explanation

Electronic configuration of `AI -1s^(2), 2s^(2) 2p^(6) 3s^(2) 3p^(6) 3p^(1)` Electronic configuration of Mg - `1s^(2) 2s^(2) 2p^(6) 3s^(2)`. It is difficult to remove electron from paired `3s^(2)` - orbital than unpaired `3p^(1)`. Hence I.E of AI is lower then Mg.