WAEC Chemistry 2017 Paper

Concept:Oxidation number is the apparent charge of an atom in a compound. For a neutral compound, the sum of all oxidation numbers is zero.Explanation:In $\mathrm{Pb(NO_3)_2}$, lead ($\mathrm{Pb}$) has an oxidation number of $+2$.Oxygen has an oxidation number of $-2$, and there are 6 oxygen atoms, contributing $6 \times (-2) = -12$.Let the oxidation number of nitrogen be $x$. Since there are 2 nitrogen atoms, the total contribution from nitrogen is $2x$.Using the rule that the total sum equals zero:$$+2 + 2x + (-12) = 0$$$$2x - 10 = 0$$$$2x = 10$$$$x = +5$$Answer:The oxidation number of nitrogen in $\mathrm{Pb(NO_3)_2}$ is $+5$, so the correct option is D.