The diagram shows an experiment that is used to determine the percentage of oxygen in $150\,\text{cm}^3$ of polluted air. The apparatus is then left for one week. After this period, the gas volume in the measuring cylinder is $122\,\text{cm}^3$. What is the percentage of oxygen, to the nearest whole number, in the polluted air?
- A19%
- B21%
- C28%
- D81%