Question

Two elements A and B combine to form compounds X and Y. For a fixed mass of A, the masses of B that combine to form the compounds X and Y are in the ratio $3:7$. If in the compound X, $4\text{g}$ of A combines with $12\text{g}$ of B, then in compound Y, $8\text{g}$ of A will combine with _______ $\text{g}$ of B.

• A. 24
• B. 56
• C. 28
• D. 8

Answer 1

The correct option is B 56

This comes under the law of multiple proportion.

Given,
$\frac{\text{Mass of B in X}}{\text{Mass of B in Y}}=\frac{3}{7}$
Let the mass of $A=z$. Therefore, mass of B in $X=3z$, mass of B in $Y=7z$
$3z=12$ (for X)
$z=4$ (mass of A)
For, $Y:z=8$ (given)
Therefore, mass of $B=7\times 8=56\text{g}$