WAEC Chemistry 2015 Paper

Concept:Electrons are negatively charged particles, so the unknown $y$ can be found by balancing the total electric charge on both sides of the equation.Explanation:Write the charge contributed by each species on the left-hand side.The sulfate ion $\mathrm{SO}_4^{2-}$ gives a charge of $-2$.Two hydrogen ions, $2\mathrm{H}^{+}$, give a total charge of $+2$.If $y$ electrons are present, their total charge contribution is $-y$, because each electron carries one unit of negative charge.Therefore, the total charge on the left-hand side is:$$(-2) + (+2) + (-y) = -y$$On the right-hand side, the sulfate ion $\mathrm{SO}_4^{2-}$ gives a charge of $-2$, and $\mathrm{H}_2\mathrm{O}$ has no net charge.So the total charge on the right-hand side is $-2$.For the equation to be balanced, the left-hand charge must equal the right-hand charge:$$-y = -2$$This gives $y = 2$.Hence, two electrons are required.Answer:The value of $y$ is $2$, so the correct option is A.