The pair of electron in the given carbanion, ${\text{CH}}_3\text{C}\equiv {\text{C}}^{\ominus }$ is present in which of the following orbitals?

In the carbanion ${\text{CH}}_3\text{C}\equiv {\text{C}}^{\ominus }$, the terminal carbon atom is involved in a triple bond (one $\sigma$ and two $\pi$ bonds) and carries a lone pair. The steric number $=1(\sigma \text{ bond})+1(\text{lone pair})=2$. Thus, the hybridization of that carbon is $sp$, and the lone pair resides in an $sp$ hybrid orbital.