Q. 4

The first ionisation enthalpies of Na, Mg, Al and Si are in the order:
A. Na < Mg > Al < Si

B. Na > Mg > Al > Si

C. Na < Mg < Al < Si

D. Na > Mg > Al < S

Answer :

Na configuration: 1s2,2s2,2p6,3s1.

Mg configuration: 1s2,2s2,2p6,3s2.


Al configuration: 1s2,2s2,2p6,3s2,3p1


Si configuration: 1s2,2s2,2p6,3s2,3p2


As effective nuclear charge on Na is less than Mg, so the ionisation enthalpy of Na will be less than Mg as Mg has 2 electrons and Na has one electron in the outermost shell.


It is easier to remove an electron from p orbital than in s orbital so the ionisation enthalpy of Mg is less than Al. Therefore, Ionisation enthalpy of Mg is greater than Al.

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