$D_2O$ is preferred to $H_2O$ as a moderator in nuclear reactors because:

Consider the following statements regarding heavy water $(D_2O)$. Which of the following statements is/are correct?
$(A)$ Heavy water is used as a moderator in nuclear reactors.
$(B)$ The power of association is higher in $D_2O$ than in ordinary water $(H_2O)$.
$(C)$ Heavy water is more effective as a solvent than ordinary water.

Temporary hardness and permanent hardness can be removed by the sequential addition of which of the following?

The ratio of the viscosity (in centipoise) of $D_2O$ to that of $H_2O$ at $25^{\circ} C$ is

Which of the following hydrides has the lowest boiling point?

Which of the following will cause softening of hard water?