Question

The composition (by atom) 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 proportion, 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

When two elements combine with each other to form more than one compound, the weight of one element combined with the weight of another element are in ratio of small whole numbers. This law says when elements in those chemical compounds can be expressed by small whole number ratios. We have the composition of compounds by atoms A and B and give the values to find the ratio of weight by law of multiple proportions.

Complete step by step answer:
Here we have the value of the composition of compound A and the composition of compound B which is in ratio of X and Y.
According to multiple proportion law, we find the ratio of weight of element Y in compounds.
The composition of compound A is $X:Y = 40:60 = 2:3$
As well as, the composition of compound B is $X:Y = 25:75 = 1:3$
Here we see that 2 moles of X combine with 3 mole of Y and 2 mole of X combine with 6 moles of Y.
So, the ratio of the weight of element Y is $3:6 = 1:2$ .
Therefore, option (A) is the correct answer.

Note: The law of multiple proportions is similar with the law of stoichiometry. This law shows the smallest possible amount of matter that still retains its identity as a chemical element, known to consist of a nucleus surrounded by electrons.