Discussion
The mass number of nucleus is:
Answer: B
The mass number is the sum of the number of protons and neutrons present in the nucleus.
The mass number A counts the nucleons: A = Z + N, where Z is the number of protons (the atomic number) and N the number of neutrons. For carbon-12, 6 protons and 6 neutrons give A = 12.
The mass number is never less than the atomic number, because it includes the protons, and for hydrogen-1 the two are equal. It is a whole number, not a fraction, since it counts particles. It is not 'always more than the atomic weight': the atomic weight is an average over isotopes and can lie above or below the mass number of a given isotope (chlorine-35 has mass number 35, below chlorine's atomic weight of 35.45).
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