Q. Heavy water is so called because it contains:
Answer: Heavy isotope of hydrogen
Notes: Heavy water, formally called deuterium oxide, is a form of water that contains a larger than normal amount of the hydrogen isotope deuterium, (also known as "heavy hydrogen") rather than the common hydrogen-1 isotope (protium) that makes up most of the hydrogen in normal water.

This question is part of 40000+ General Studies MCQ Series Course on GKToday Android app. Question Number: 58 in Chemistry-4-Compounds in above course in App.