BECE Science 2021 Paper

Concept:A chemical equation is balanced when the number of atoms of each element is equal on both the reactant and product sides.Explanation:Check every option by counting atoms on each side.Option A: $\mathrm{H}_2 + \mathrm{Cl}_2 \rightarrow \mathrm{HCl}$Left side has 2 hydrogen and 2 chlorine atoms.Right side has 1 hydrogen and 1 chlorine atom.So, this equation is not balanced.Option B: $\mathrm{K}_2\mathrm{O} \rightarrow \mathrm{K} + \mathrm{O}_2$Left side has 2 potassium and 1 oxygen atom.Right side has 1 potassium and 2 oxygen atoms.So, this equation is not balanced.Option C: $\mathrm{Mg} + \mathrm{O}_2 \rightarrow \mathrm{MgO}$Left side has 1 magnesium and 2 oxygen atoms.Right side has 1 magnesium and 1 oxygen atom.So, this equation is not balanced.Option D: $2\mathrm{Na} + \mathrm{Cl}_2 \rightarrow 2\mathrm{NaCl}$Left side has 2 sodium atoms and 2 chlorine atoms.Right side has 2 sodium atoms and 2 chlorine atoms.Since the numbers match on both sides, this equation is balanced.Answer:Option D: $2\mathrm{Na} + \mathrm{Cl}_2 \rightarrow 2\mathrm{NaCl}$