Mass number A is:
AAtomic mass
BNumber of PROTONS + NEUTRONS (= Z + N)
CCharge
DNumber of electrons
Answer & Solution
Correct answer: B. Number of PROTONS + NEUTRONS (= Z + N)
A = Z + N (nucleons total). Notation ^A_Z X: e.g., ^12_6 C has 6 protons + 6 neutrons; ^14_6 C has 6 protons + 8 neutrons (carbon-14 isotope).
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