Compound X is made up of carbon, hydrogen and oxygen only. Its $M_r$ is $90$. In $100\,\text{g}$ of compound X, there are $40.0\,\text{g}$ of carbon and $6.7\,\text{g}$ of hydrogen. How many oxygen atoms are present in one molecule of compound X?
- A1
- B2
- C3
- D4