Q. Which one of the following was used as a chemical weapon in the First World War? (UPSC Prelims 1997)
Answer: Mustard gas
Notes: 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.