The first ionisation potential of aluminium is smaller than that of magnesium because
A.
Atomic size of $$Al >$$ Atomic size of $$Mg.$$
B.
Atomic size of $$Al <$$ Atomic size of $$Mg.$$
C.
$$Al$$ has one electron in $$p$$ - orbital
D.
None of these
Answer :
$$Al$$ has one electron in $$p$$ - orbital
Solution :
$$Al\left( {3{s^2}{p^1}} \right)$$ and $$Mg\left( {3{s^2}} \right).$$ Lower energy is required to remove $$3{p^1}$$ electron than $$3{s^1}$$ electron ( penetrating effect is $$s > p > d > f\,).$$
Secondly $$Mg$$ has stable electronic configuration than $$Al$$
Releted MCQ Question on Inorganic Chemistry >> Classification of Elements and Periodicity in Properties
Releted Question 1
The correct order of second ionisation potential of carbon, nitrogen, oxygen and fluorine is