Question

In a nuclear reaction some mass converts into energy. In this reaction total B.E of reactants when compared with that of products is:
A. Always greater
B. Always less
C. Either greater or less
D. Always equal

Answer 1

Consider the term binding energy, it denotes to the energy that is essential to bind two entities. Here, the nature of the two entities is defined by the fact that these two terms are from a nuclear physics background. At this instant try to relate mass and energy to define what mass defect may mean.

Complete step by step answer:
When we measure the weight of an atomic nucleus, it is observed that the measured weight will always be slightly less than that of the calculated weight which is obtained by the sum of masses of all protons and neutrons present in the nucleus. This difference in the observed and theoretical weights is known as the mass defect.
Binding energy refers to the energy that is required to separate sub-atomic particles or crystal lattices from each other. In this context, we will be talking about protons and neutrons. A system that is bound together typically has lower energy than free-floating particles.
These terms are said to be related in a way that the mass defect is considered to be the binding energy. The difference in the observed weight and the calculated weight is accounted for by the binding energy. It is a bit hard to instinctively predict how energy having mass works. So we use the following formula to facilitate the conversion:
$E=m{{c}^{2}}$
This formula is used to calculate the binding energy of each nucleus using the mass defect as they are seen to be equivalent. Einstein proved that this conversion is possible in his special theory of relativity.
Therefore, the binding energy of the products is always greater than the binding energy of the reactants, and the difference between them is released as energy.
Thus, from the above discussion, we can conclude that the binding energy of reactants, when compared with that of products in a nuclear reaction, is always less.
Hence, the correct answer is option (B).

Note: Please do not confuse these terms with the ones in crystal lattices. Although crystal lattices have binding energy too, no mass defect is found in them. Hence, we will assume that this question talks about the nuclear and sub-atomic aspect of both these terms.