Q. Who among the following discovered heavy water? (UPSC Prelims 2008)
Answer: H. C. Urey
Notes: Heavy water (deuterium oxide, D₂O) was discovered by Harold Clayton Urey, known as H. C. Urey, in 1931. Urey, an American chemist, isolated deuterium (²H) using fractional distillation and electrolysis of water, earning the 1934 Nobel Prize in Chemistry for this isotope discovery. The other scientists mentioned made significant contributions in different fields: Heinrich Hertz discovered electromagnetic waves; Gregor Mendel founded genetics; Joseph Priestley isolated oxygen. None of these relate to heavy water.