Question

In a nuclear power plant, coolant is a substance:

(a) which cools the hot, spent steam to condense it back to water
(b) which transfers heat from reactor to water in heat exchanger
(c) which is boiled to make steam to turn the turbine
(d) which cools the generator coils to prevent their overheating.

Answer 1

which transfers the heat from the reactor to the water in the heat exchanger

Liquid sodium or carbon dioxide gas is used as a coolant.