The mass deficit primarily affects the nucleus of an atom.
The mass of an atom is primarily concentrated in its nucleus, which is composed of protons and neutrons. Protons have a positive charge, while neutrons are neutral. These subatomic particles contribute to the mass of the nucleus.
The mass deficit refers to the difference in mass between the sum of the individual masses of protons and neutrons in the nucleus and the actual measured mass of the nucleus. This discrepancy arises due to the binding energy required to hold the protons and neutrons together in the nucleus.
According to Einstein's mass-energy equivalence principle (E = mc²), the binding energy is equivalent to a mass difference. The mass defect or mass deficit represents the "lost" mass that has been converted into binding energy, as described by Einstein's equation. This conversion occurs due to the strong nuclear force, which is responsible for holding the nucleus together.
In summary, the mass deficit affects the nucleus of an atom, representing the difference in mass between the sum of individual nucleons (protons and neutrons) and the actual measured mass of the nucleus, due to the conversion of mass into binding energy.