The unit of atomic mass, $\mathrm{amu}$ is replaced by $\mathrm{u}$, here $\mathrm{u}$ stands for

In the reaction $2{\mathrm{KClO}}_{3\left(\mathrm{s}\right)}⟶2{\mathrm{KCl}}_{\left(\mathrm{s}\right)}+3{\mathrm{O}}_{2\left(\mathrm{g}\right) }{\mathrm{\Delta H}}^o=-78 \mathrm{kJ}$. If $33.6 \mathrm{L}$ of oxygen gas is liberated at $\mathrm{S}.\mathrm{T}.\mathrm{P}.$ What is the mass of ${\mathrm{KCl}}_{\left(\mathrm{s}\right)}$ produced ? (atomic mass $\mathrm{K}=39, \mathrm{Cl}=35.5 \mathrm{g} {\mathrm{mol}}^{-1}$)