Question

Heavy water is
A. Water with mercury compounds
B. Water with chlorides and sulphates of $Ca$ and $Mg$
C. Water with bicarbonates of $Ca$ and $Mg$ .
D. Deuterium oxide.

Answer 1

Water that contains heavy hydrogen is heavy water. Heavy water is naturally present, but in much smaller amounts than normal water. For every twenty million molecules of water, approximately one water molecule is heavy water.

Complete step by step answer:
Heavy water has the chemical formula ${D_2}O$ . It is also called deuterium oxide. It is different from water because it contains a heavy isotope of hydrogen.
Isotopes of an element have the same atomic number but different atomic mass number. There are three isotopes of hydrogen- $_1^1H(protium),_1^2D(deuterium),_1^3T(tritium)$ .
Protium consists of one electron, one proton and no neutron. It is most abundantly available.
$_1^2D$ stands for deuterium. It has atomic number one and atomic mass number two. It has one proton, one neutron and one electron. The atomic mass number is double that of hydrogen.
Tritium has one proton, two neutrons and one electron. It is the radioactive isotope of hydrogen.
Heavy water is not a radioactive compound. Heavy water is $10\%$ heavier than the normal water.
Heavy water is used in nuclear reactors. The chain reactions going on in nuclear reactors are kept going with the help of heavy water. It is prepared artificially.
Heavy water does not contain any mercury compounds or carbonates or sulphates. It is just deuterium oxide.

So, the correct answer is “Option D”.

Note:
Deuterium and its compounds are used as non-radioactive labels in $^1H - NMR$ spectroscopy.
In spectroscopy, a deuterated solvent is used so that the hydrogen atoms get labelled.
Deuterium is also used as a fuel for nuclear fusion. The atomic mass number is double that of hydrogen.