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The mass number of an atom is the sum of its protons and:
ANeutrons
BElectrons
CPositrons
DNucleotides
Answer & Solution
Correct answer: A. Neutrons
1. Electrons are far too light to count.
2. Only nuclear particles matter here.
3. It is protons plus neutrons.
_Source: NCERT Class 9 Science, Ch 4 'Structure of the Atom'_
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