Answer: Option (b) is the correct answer.
Step-by-step explanation:
When a substance resists or does not allow any flow of electric current through it then it is known as an insulator.
For example, rubber, glass, paper etc are all insulators.
A conductor is a substance that allows easy passage of electric current through it.
A radiator is defined as the substance which emits radiations to transfer heat energy for heating and warming purpose.
A solar collector collects radiations that are passed from the Sun.
Thus, we can conclude that an insulator is a material that reduces the flow of heat by conduction, convection, and radiation.