Who among the following discovered heavy water?

The correct answer is H. C. Urey (option 2). Harold C. Urey discovered deuterium, the heavy isotope of hydrogen, in the winter of 1931; this isotope is the basis of heavy water (D2O) and Urey’s work directly led to its identification [1]. Urey enriched and detected the heavier hydrogen isotope by techniques such as fractional distillation of liquid hydrogen, confirming the existence of deuterium and thereby establishing the composition of heavy water (deuterium oxide). His discovery of heavy hydrogen was recognized with a Nobel Prize, linking him definitively to the discovery and characterization of heavy water’s constituent isotope [2].

Sources

1. [1] https://www.sciencedirect.com/book/9780128110409/deuterium
2. [2] https://www.chm.bris.ac.uk/motm/D2O/D2Ov.htm