Question 9 rank the effective nuclear charge z * experienced by a valence electron in each of these atoms:

To rank the effective nuclear charge Z * experienced by a valence electrons of a set of atoms that belong to a same period, you only need to apply the rule of trend: it increases as you move from left to right in the period.

So, lets do it for these atoms: P, Al, Si, Cl

The belong to a same period and the order is Al, Si, P, Cl (just see a periodic table). So the rank is Al < Si < P < Cl

Now, lets do it for these atoms:, Be, Ne, O, C

They belong to the second period. The order is Be, C, O, Ne

So, the rank is Be < C < O < Ne.