\(C _{2} H _{5}- Cl + \underset{(alc)}{KCN} \stackrel{\Delta}{\longrightarrow} C _{2} H _{5}- CN + KCl\)
Hence, to obtain propanenitrile, \(R- Cl\) should be chloroethane.
The hydrocarbons such as Haloalkanes and Haloarenes are the ones, in which one or more hydrogen atoms are replaced with halogen atoms. The main difference between Haloalkanes and Haloarenes is that Haloalkanes are derived from open chained hydrocarbons, also called alkanes, and Haloarenes are derived from aromatic hydrocarbons.