WAEC Chemistry 2013 Paper

Concept:The position of an element in the periodic table is determined by its electron configuration: the block by the last orbital, the period by the highest shell number, and the group by the total valence electrons.Explanation:The total number of electrons is $2 + 2 + 6 + 2 + 1 = 13$.The electron arrangement by shells is $2, 8, 3$.The highest occupied principal quantum number is $3$, so the element lies in period $3$.The last electron enters the $3p$ subshell, so the element belongs to the p-block.The total number of valence electrons is $2$ (from $3s^2$) $+ 1$ (from $3p^1$) $= 3$, so the element belongs to group $3$.This element is aluminium, $\mathrm{Al}$.Answer:D. p-block, period 3, group 3