Question

3)The sum of the numbers of protons and neutrons of an atom

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Answer 1

Answer:

$number \: of \: proton + neutron \\ \\ = atomic \: number$

hope it helps uH ✔

Answer 2

Answer

The sum of the number of protons and neutrons of an atom is called the mass number.For example.

Carbon-12 has 12 protons and 12 neutrons

12+12=24,so the mass number of C-12 is 24(no units).