Question
The first ionisation potential of $$Na,Mg,Al\,\,{\text{and}}\,\,Si$$ are in the order
A.
$$Na < Mg > Al\, < \,Si$$
B.
$$Na > Mg > Al\, > Si$$
C.
$$Na < Mg < Al\, < Si$$
D.
$$Na > Mg > Al\, < Si$$
Answer :
$$Na < Mg > Al\, < \,Si$$
Solution :
NOTE : First ionisation potential increases from left to right in a period, But $$Mg$$ is more stable than $$Al$$ due to fully filled-$$3s$$ orbitals.
$$I{E_1}$$ of $$Mg$$ is higher than that of $$Na$$ because of
increased nuclear charge and also that of $$Al\,$$ because
in $$Mg$$ a $$3$$ $$s$$-electron has to be removed while in $$Al\,$$ it is
the $$3$$ $$p$$-electron. The $$I{E_1}$$ of $$Si\,$$ is, however, higher than those of $$Mg$$ and $$Al$$ because of its increased nuclear
charge. Thus, the overall order is $$Na < Mg > Al\, < \,Si$$