${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH} \underset{\mathrm{Cu}}{\overset{300°\mathrm{c}}{\to }} {\mathrm{CH}}_3\mathrm{CHO}$

The above process is

When vapours of a 1° or 2°alcohol are passed over Cu or Ag catalyst at ${300}^{\mathrm{o}}\mathrm{C}$, dehydrogenation takes place. In presence of these catalysts, if air is present then water is formed along with carbonyl compound. It is a better method of preparation because further oxidation takes place.

Hence, the correct option is: (C) Dehydrogenation.