Ethylamine undergoes oxidation in the presence of ${\mathrm{KMnO}}_4$followed by hydrolysis to form. 

• Amines undergo oxidation in the presence of different oxidizing agents to yield various products. The products mostly depend on the oxidizing agents used. ${\mathrm{KMnO}}_{4^{\text{'}}}$ potassium permanganate is a strong oxidizing agent 
• when ethylamine which is a primary amine is treated with ${\mathrm{KMnO}}_4$ it yields an aldehyde as a product.${\mathrm{CH}}_3-{\mathrm{CH}}_2-{\mathrm{NH}}_2+{\mathrm{KMnO}}_4\to {\mathrm{CH}}_3-\mathrm{CH}\equiv \mathrm{NH}+{\mathrm{H}}_3{\mathrm{O}}^{+}\to {\mathrm{CH}}_3\mathrm{CHO}$

Ethyl amine when reacts with potassium permanganate, forms aldimine which further on hydrolysis gives acetaldehyde.

Therefore, option (C) is correct.