Question

What is the percent $X$ by mass for compound $X{Y}_2$ if compound $XY$ is $74$% $X$ by mass?

• A. $25$%
• B. $40$%
• C. $60$%
• D. $75$%

Answer 1

The correct option is C $60$%

Given $\%$ of X in $XY=74\%$

So, $\%$ Y in $XY=26\%$

$\Rightarrow \frac{\text{Mass of X}}{\text{Mass of X + Mass of Y}}=\frac{74}{100}$

$\Rightarrow 100\text{mass of X}=74\left(\text{mass of X}\right)+74\left(\text{mass of Y}\right)$

$\Rightarrow 26\text{mass of X}=74\left(\text{mass of Y}\right)$

$\Rightarrow 13\text{mass of X}=37\left(\text{mass of Y}\right)$

$\%$ of X in $X{Y}_2=\frac{\text{Mass of X}}{\text{(Mass of X) + 2(Mass of Y)}}\times 100=\frac{\frac{37}{13}\left(\text{Mass of Y}\right)}{\frac{63}{13}\left(\text{Mass of Y}\right)}\times 100=\frac{37}{63}\times 100=60\%$