Which one of the following was used as a chemical weapon in the first world war ?

A. Carbon monoxide

B. Hydrogen cyanide

C. Mustard gas

D. Water gas

Answer: Option C

Solution(By Examveda Team)

Although the Germans were the first to use phosgene on the battlefield, it became the primary chemical weapon of the Allies. Phosgene was responsible for 85% of chemical-weapons fatalities during World War I. Mustard gas, a potent blistering agent, was dubbed King of the Battle Gases.