To find the volume a swallowed drop of liquid oxygen occupies as gas at 37°C, the order of working is:

1. The drop is given by its volume and density, so mass comes first: $m=\rho v$. 2. Convert that mass to moles using $n=\dfrac{m}{M_r}$, with $M_r=32$ for oxygen. 3. Substitute $n$ into $PV=nRT$ with $T=310$ K and $P=1$ atm. 4. Rearranging gives $V=\dfrac{nRT}{P}$, the volume of gas produced. 5. Any order that needs moles before mass cannot start, because moles are derived from the mass. _Source: NECTA ACSEE 2023 Chemistry 132/1, Question 1: Gases_