The mass defect is the result of what action occurring? A. Mass being converted to energy when protons and neutrons bind together in a nucleus B. Protons and electrons being attracted to each other C. Energy being converted into moles of atoms when neutrons break apart protons D. Mass being converted to energy when protons and neutrons break apart in a nucleus

The correct answer is: A. Mass being converted to energy when protons and neutrons bind together in a nucleus.

Mass defect is the difference between the mass of an atom and the sum of the masses of its constituent protons, neutrons, and electrons. This difference is due to the binding energy that holds the nucleus together. The binding energy is released when the nucleus is formed, and it appears as a difference in mass.

Option B is incorrect because protons and electrons are not attracted to each other. In fact, they have a repulsive force due to their positive and negative charges.

Option C is incorrect because energy is not converted into moles of atoms when neutrons break apart protons. When a neutron decays, it releases an electron and an antineutrino. The electron and antineutrino are not atoms, and they do not have a mass that is equivalent to the mass of the neutron.

Option D is incorrect because mass is not converted to energy when protons and neutrons break apart in a nucleus. When a nucleus decays, it releases energy in the form of gamma rays. The gamma rays have a mass that is much less than the mass of the nucleus.