A triple bond is found in which of the following species?

(P)$\mathrm{CO}$ (R) ${\mathrm{C}}_2{\mathrm{H}}_2$ (Q) ${\mathrm{CN}}^{-}$

The structure of the given molecules,

$$\begin{gathered} \overline{\mathrm{C}}\equiv \stackrel{+}{\mathrm{O}} \\ ,\mathrm{H}-\mathrm{C}\equiv \mathrm{C}-\mathrm{H}, \\ \mathrm{C}=\mathrm{N} \end{gathered}$$

Thus, triple bond is found in all of the given species.