On the atomic scale, the atomic weight of $\mathrm{Ca}$ is $40$ $\mathrm{u}$. If one $\mathrm{u}$ is redefined as per the question, which of the following would be correct?

Drug marijuana owes its activity to tetrahydrocannabinol, which contains $70\%$ as many as carbon atoms as hydrogen and $15$ times as many hydrogen atoms as oxygen. In a gram of tetrahydrocannabinol, the number of moles is $0.00318$. Determine its molecular formula.

At $\mathrm{NTP}$, the density of ${\mathrm{O}}_2$ is $1.429 \mathrm{g}/\mathrm{L}$. Calculate the standard molar volume of gas.

Oxygen is exploded with a gaseous alkane. For complete combustion to ${\mathrm{CO}}_2$, the volume of ${\mathrm{O}}_2$ consumed is in the ratio $7:4$.  Deduce the molecular formula of alkane.