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Chemistry Question on Classification

In the 3rd3^{rd} period, the first ionisation potential is of the order

A

Na>Mg>Al>Si>P{ Na > Mg > Al > Si > P }

B

Mg>Na>Si>P>Al{ Mg > Na > Si > P > Al }

C

Na<Mg<Al<Si<P{ Na < Mg < Al < Si < P }

D

Na<Al<Mg<Si<P{ Na < Al < Mg < Si < P }

Answer

Na<Al<Mg<Si<P{ Na < Al < Mg < Si < P }

Explanation

Solution

Ionisation potential increases across a period with increasing atomic number. But Mg (1s22s22p63s2){ Mg }\, (1s^22s^22p^63s^2) has higher ionisation enthalpy than Al(1s22s22p63s23p1){Al }(1s^22s^22p^63s^23p^1) due to stable fully filled orbitals of magnesium. Thus, the correct order is :
1st I.E ({kJmol^{-1}}) : {\underset{\mathrm{496}}{{Na}}<<\underset{\mathrm{577}}{{Al}}<<\underset{\mathrm{737}}{{Mg}}<<\underset{\mathrm{786}}{{Si}}<<\underset{\mathrm{1011} }{{P}}}