Question

A compound contains $3.2\%$ of oxygen. Find the minimum molecular weight of the compound.

Answer 1

Answer: 500

The compound must contain at least one oxygen atom. So, a minimum of $1g$ atom of oxygen will be present in $1g$ molecule, i.e., $1mol$ of the compound.
If $M$ is the molecular weight of the compound, then since $16$ is the atomic mass of oxygen, so minimum of $16g$ of oxygen will be present in $M$ gram of the compound.
Thus, \% of oxygen $=\frac{16}{M}\times 100$
or $3.2=\frac{16\times 100}{M}$ or $M=500$