The reaction ${\mathrm{CH}}_3\mathrm{I}+{\mathrm{C}}_2{\mathrm{H}}_5\mathrm{ONa}\to {\mathrm{CH}}_3{\mathrm{OC}}_2{\mathrm{H}}_5+\mathrm{NaI}$ is an example of 

The reaction ${\mathrm{CH}}_3\mathrm{I}+{\mathrm{C}}_2{\mathrm{H}}_5\mathrm{ONa}\to {\mathrm{CH}}_3{\mathrm{OC}}_2{\mathrm{H}}_5+\mathrm{NaI}$ is an example of  Williamson synthesis.

The Williamson synthesis is a way to make ethers by reacting sodium alkoxide with ethyl cellulose, an alkyl halide that is a halogen derivative of a hydrocarbon.

Hence, correct option is C.