Hydrogen cyanide (HCN) is a linear molecule. The carbon and nitrogen are connected by a triple bond, and the hydrogen is connected to the carbon atom with a single bond. If you were to look at the molecule in terms of its bond angles, the H-C-N bond angle is 180 degrees, which is characteristic of linear molecules. This linear geometry is a result of the sp hybridization of the carbon atom, which arranges the electrons in two linearly opposing sp orbitals.
