Which of the substances listed below will combust? Explain your reasoning.
$\begin{array}{ll}{\text { a. } \mathrm{Na}_{2} \mathrm{SO}_{4}(s)} & {\text { b. } \mathrm{Cu}(s)} & {\text { c. } \mathrm{MgO}(s)} \\ {\text { d. } \mathrm{Na}(s)} & {\text { e. } \mathrm{C}_{2} \mathrm{H}_{6} \mathrm{O}(l)} & {\text { f. } \mathrm{Ar}(g)}\end{array}$