BECE Science 2026 Paper

Concept:A stable compound is formed when the total positive valency equals the total negative valency, so the valencies are swapped as subscripts.Explanation:Sodium has a valency of $1$ and oxygen has a valency of $2$.Write the symbols with their valencies: $Na^{1}$ and $O^{2}$.Using the criss-cross method, the valency of oxygen, $2$, becomes the subscript of sodium: $Na_2$.The valency of sodium, $1$, becomes the subscript of oxygen: $O_1$.Subscript $1$ is not written in a final formula, so the formula becomes $Na_2O$.In $Na_2O$, two sodium atoms each give $+1$, giving a total of $+2$, which balances oxygen’s $-2$.Therefore, $Na_2O$ is the stable compound formed.Answer:B. $Na_2O$