If the molecular mass of a compound is $M$ and the mass of an element present in one molecule is $X$, the percentage of that element in the compound is
A$\dfrac{M}{X}\times 100$
B$\dfrac{X}{M}$
C$\dfrac{X}{M}\times 100$
D$\dfrac{100}{M\times X}$
Answer & Solution
Correct answer: C. $\dfrac{X}{M}\times 100$
Percentage composition is defined as the mass of the element divided by the molecular mass of the compound, multiplied by 100. Hence the correct expression is $\dfrac{X}{M}\times 100$.