JAMB Chemistry 2024 Paper

Concept:The principal quantum number $n$ gives the energy level or shell of an electron.The maximum number of electrons that can occupy a shell is given by $2n^2$.Explanation:For $n = 3$, substitute into the formula:$$2n^2 = 2(3)^2$$$$= 2 \times 9$$$$= 18$$The $n=3$ shell contains the $3s$, $3p$, and $3d$ subshells.Their electron capacities are $2$, $6$, and $10$ respectively, giving a total of $2 + 6 + 10 = 18$.Therefore, when $n = 3$, the shell can hold up to $18$ electrons.Answer:C. $18$