WAEC Chemistry 2012 Paper

Concept:When two elements form more than one compound, the masses of one element that combine with a fixed mass of the other are in a ratio of small whole numbers.Explanation:Metal $M$ forms two chlorides: $MCl_2$ and $MCl_3$. In both chlorides, the mass of $M$ is fixed as one atom of $M$. The mass of chlorine combined with this fixed mass of $M$ is $2$ atoms in $MCl_2$ and $3$ atoms in $MCl_3$. Thus, the ratio of chlorine masses is $2 : 3$, which is a ratio of small whole numbers. This relationship is best explained by the law of multiple proportion.Answer:C. multiple proportion