Which of the following statements regarding heavy water are correct? 1. It is extensively used as a moderator in nuclear reactors 2. It cannot be used in exchange reaction to study reaction mechanism 3. Viscosity of heavy water is relatively smaller than that of ordinary water 4. The dielectric constant of heavy water is smaller than that of ordinary water Select the correct answer using the code given below:

Heavy water (D2O) is extensively used as a moderator in nuclear reactors, such as Pressurized Heavy Water Reactors (PHWRs), to slow down neutrons [2]. Statement 1 is therefore correct. Regarding statement 2, heavy water is frequently used in exchange reactions to study reaction mechanisms and kinetic isotope effects, as deuterium can replace hydrogen in various compounds. Statement 3 is incorrect because the viscosity of heavy water (1.25 cP at 20°C) is actually higher than that of ordinary water (1.00 cP). Statement 4 is correct; the dielectric constant of heavy water is slightly lower (approximately 78.06) compared to ordinary water (78.39). This difference arises from the stronger hydrogen bonding and different dipole moments in D2O. Since statements 1 and 4 are correct, the correct option is 4.

Sources

1. [1] https://hwb.gov.in/frequently-asked-questions-faqs
2. [2] https://pubmed.ncbi.nlm.nih.gov/10535697/