Answer: Option (B) is the correct answer.
Step-by-step explanation:
Plasma is the hot gas which is ionized and has equal number of both positive ions and negatively charged electrons.
To carry out nuclear fusion reaction it is necessary to provide high temperature. Though there is high temperature so, gases present in the reaction will also reach at high temperature.
Therefore, these gases will convert into plasma.
Thus, we can conclude that achieving high temperatures and containing the plasma reactants are the problems that must be overcome before fusion can be used to produce energy.