Question

Trudy writes an expression to calculate the mass defect of a carbon-14 nucleus using the symbols in the table.

A 2 column table with 4 rows. The first column is labeled quantity with entries mass of carbon-14 nucleus, mass of proton, mass of neutron, mass of electron. The second column is labeled symbol with entries m Subscript C-14 baseline, m Subscript p baseline, m Subscript n baseline, m Subscript e baseline.
Which expression should Trudy write?

(6mp + 8mn) – mc – 14
(8mp + 6mn) – mc – 14
mp + mn – mc – 14
6mp + 8me – mc – 14

Answer 1

(6m_p + 8m_n) − m_{C-14}

Reason: C-14 nucleus has 6 protons and 8 neutrons, and mass defect = (sum of masses of separate nucleons) − (actual nuclear mass). Electrons are not part of the nucleus.