A nucleus is NMR active if its nuclear spin quantum number $I \neq 0$.
- $^1$H has $I = \frac{1}{2}$ → NMR active.
- $^{13}$C has $I = \frac{1}{2}$ → NMR active.
- $^{16}$O has $I = 0$ → NMR inactive.
- $^{32}$S has $I = 0$ → NMR inactive.
Thus, only $^1$H and $^{13}$C are NMR active.