JAMB Chemistry 2014 Paper

Concept:The element's valence-shell configuration determines its group and chemical family.Explanation:The electron configuration is $1\mathrm{s}^2\,2\mathrm{s}^2\,2\mathrm{p}^6\,3\mathrm{s}^2\,3\mathrm{p}^5$.The outermost shell is $n=3$, containing $2+5=7$ electrons.A p-subshell is completely filled only when it has $6$ electrons; here it has $5$, so it is not completely filled.With $7$ valence electrons, the element belongs to group 17 and is a halogen (chlorine).Therefore, statement D is correct.Answer:D. It is a halogen.