Mass number of an atom equals
AProtons plus electrons in the atom
BProtons plus neutrons in the nucleus
CNeutrons minus protons in the nucleus
DElectrons in the outermost shell
Answer & Solution
Correct answer: B. Protons plus neutrons in the nucleus
1. The chapter defines mass number A.
2. Almost all of an atom's mass sits in the nucleus.
3. Electrons are very light and ignored in this count.
4. So mass number = protons + neutrons.
_Source: Selina Concise Chemistry Class 8, Ch on Structure of Atom (Mistral OCR'd PDF), section on mass number_
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