(solved)Question 2.65 of NCERT Class XI Chemistry Chapter 2

Write the electronic configurations first

$\displaystyle \text{Al is: } 1s^22s^22p^63s^23p^1$

$\displaystyle \text{Si is: } 1s^22s^22p^63s^23p^2$

we have to compare same orbitals, i.e., 3p

both orbitals are shielded by the same
number of electrons, i.e., $\displaystyle 1s^22s^22p^63s^2$

$\displaystyle \therefore$ nuclear charge (Z) is the deciding factor

$\displaystyle Z_{Al} = 13$ and $\displaystyle Z_{Si} = 14$

Since Si has more protons, each 3p electron
of Si experiences more effective nuclear charge