Question

First ionisation enthalpy of $Al$ is lower than that of $Mg$. This is because

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

Answer 1

Answer: (C)

Electronic configuration of $Al - 1s^2 2s^2 2p^6 3s^2 3p^1$
Electronic configuration of $Mg - 1s^22s^22p^63s^2$
It is difficult to remove electron from paired $3s^2$-orbital than unpaired $3p^1$. Hence, $I.E.$ of $Al$ is lower than $Mg$.