Heavy Water is so called because: A. Its density is three times that of normal water B. It uses Deuterium, a heavier isotope of hydrogen, rather than Protium C. It is used by the heavy industries such as steel, chemicals etc D. It is used in nuclear reactors

The correct answer is: B. It uses Deuterium, a heavier isotope of hydrogen, rather than Protium.

Heavy water is water that contains a higher than normal proportion of the heavy isotope of hydrogen, deuterium. It is also called deuterium oxide. The chemical formula of heavy water is $D_2O$, while the chemical formula of normal water is $H_2O$.

Heavy water is denser than normal water because the deuterium atom is heavier than the hydrogen atom. The density of heavy water is 1.107 grams per cubic centimeter, while the density of normal water is 0.997 grams per cubic centimeter.

Heavy water is not used by heavy industries such as steel, chemicals, etc. It is used in nuclear reactors as a moderator and coolant. It is also used in research and medical applications.

Here is a brief explanation of each option:

• Option A: Heavy water is not three times denser than normal water. The density of heavy water is 1.107 grams per cubic centimeter, while the density of normal water is 0.997 grams per cubic centimeter.
• Option B: Heavy water uses deuterium, a heavier isotope of hydrogen, rather than protium. This is the correct answer.
• Option C: Heavy water is not used by heavy industries such as steel, chemicals, etc. It is used in nuclear reactors as a moderator and coolant. It is also used in research and medical applications.
• Option D: Heavy water is used in nuclear reactors as a moderator and coolant. It is also used in research and medical applications. This is not the correct answer because it does not explain why heavy water is called heavy water.