Question

A neutron and a proton combine to form a nucleus. How does the mass of the nucleus compare with the sum of the masses of its individual particles?
A.The nucleus has more mass, because matter is converted into binding energy. B.The nucleus has less mass, because matter is converted into binding energy. C.The nucleus has more mass, because binding energy is converted into matter. D.The nucleus has less mass, because binding energy is converted into matter.

Answer 1

Well, just so you know, the physics presented is a bit iffy: free neutrons quickly beta- decay into protons because the difference in mass is greater than the mass of an electron. So a star, for example, will be full of protons that collide and combine at random and then split apart because the di-proton is unstable. Sometimes a di-proton will beta+ decay into a deuteron, which is how you get the nucleus in the question.

ANYWAY:

So you must be familiar with \(E=mc^2\) right? Mass can be converted into energy and vice versa (as it says in all of the possible answers). Well if you look at them, only two of the answers make sense.

They are
B: less mass because some of the mass is now energy
and
D: more mass because some of the energy is now mass

So now you consider the fact that we've gone from an unbound state to a bound state. Do you think the binding energy has increased or decreased?

Answer 2

B.The nucleus has less mass, because matter is converted into binding energy.

It takes energy to fuse a nucleus together. The energy comes at the expense of mass as mass is converted to energy. That is why nuclear bombs work so well. They convert mass to pure energy in the fusion process which is about 1 million times stronger than chemical reactions for the same mass