Question

Mass number is the number of electrons in
the nucleus of an atom.
ni​

Answer 1

Answer:

mass number= 9

Explanation:

Its nucleus also contains two neutrons. Since 2 + 2 = 4, we know that the mass number of the helium atom is 4. Finally, the helium atom also contains two electrons since the number of electrons must equal the number of protons.

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Answer 2

Answer:

Please see above attachment

Explanation:

Hope this helps you

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