The correct answer for Heavy water implies is option 3, deuterated water.
Option 1, water which is used in heavy industries such as thermal power plants, is incorrect. Heavy water is not specifically used in heavy industries such as thermal power plants. Heavy water, or deuterium oxide, is a form of water that contains a higher concentration of the isotope deuterium, which is a heavier form of hydrogen.
Option 2 states that heavy water contains SO4 and Cl of calcium and magnesium. This is also incorrect. Heavy water does not contain these specific ions. It is the isotope composition that determines whether water is classified as heavy water or regular water.
Option 4, water which has maximum density, is not entirely accurate. Heavy water actually has a slightly lower density compared to regular water due to the increased mass of the deuterium isotope.
In summary, heavy water refers to deuterated water, which contains a higher concentration of the isotope deuterium. It is not specifically used in heavy industries or characterized by specific ions or maximum density.