Chapter 31 - Atomic Physics - Conceptual Questions - Page 1111: 13

Please see the work below.

We know that the given elements have similar configurations and the outermost configurations of these elements is $2p^5,3p^5 and \space 4p^5$. All of these elements have a similar outer shell configuration (of the form $ns^2 np^5$), which is why they have similar chemical behavior.