Option (D) is correct.
The difference in mass when one type of matter is converted into another is called mass defect.
In both nuclear fusion and nuclear fission reaction, sum of masses of all the products is less than the sum of masses of all the reactants.This decrease is mass is called as mass defect. This mass equal to the mass defect is converted into energy in accordance with the Einstein's mass energy equivalence E= Δm c²
E= Energy released during the nuclear reaction
Δm= mass defect.
c= velocity of light
Thus it is the mass that gets concerted into the energy during nuclear reactions.
