Question

The composition (by atoms) of compound A is $40$% X and $60$% Y. The composition (by atoms) of compound B is $25$% X and $75$% Y. According to the law of multiple proportions, the ratio of the weight of element Y in compounds A and B is:

• A. $1:2$
• B. $2:1$
• C. $2:3$
• D. $3:4$

Answer 1

The correct option is A $1:2$

The composition of compound A is $X:Y=40:60=2:3$

The composition of compound B is $X:Y=25:75=1:3$

According to the law of multiple proportions,

In compound A, $2$ moles of $X$ bind with $3$ moles of $Y$.

In compound B, $2$ moles of $X$ bind with 6 moles of $Y$

The ratio of the weight of element $Y$, in combining with a fixed number of $X$ atoms, in these two compounds $A$ and $B$ is $3:6=1:2$.