A neutral carbon atom has Z = 6, A = 12 and atomic mass M(atom) = 12.0000 u. Take mₚ = 1.0073 u, mₙ = 1.0087 u and mₑ = 0.00055 u. The mass defect of its nucleus is approximately:
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Question

A neutral carbon atom has Z = 6, A = 12 and atomic mass M(atom) = 12.0000 u. Take mₚ = 1.0073 u, mₙ = 1.0087 u and mₑ = 0.00055 u. The mass defect of its nucleus is approximately:

G1 Physics · Accepted Answer

A neutral carbon atom contains 6 electrons. Electron mass contained in the atomic mass: 6mₑ = 6(0.00055) = 0.0033 u. Therefore, M(nucleus) = M(atom) − 6mₑ = 12.0000 − 0.0033 = 11.9967 u. The carbon-12 nucleus contains 6 protons and 6 neutrons. Mass of separated nucleons: M(free) = 6mₚ + 6mₙ = 6(1.0073) + 6(1.0087) = 6.0438 + 6.0522 = 12.0960 u. Hence, Δm = M(free) − M(nucleus) = 12.0960 − 11.9967 = 0.0993 u. Correct option: B.