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Question
Helium atom has an atomic mass of 4 u and two protons in its nucleus. How many neutrons does it have?
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Solution
Atomic mass = 4u
Atomic mass = Number of neutrons + Number of protons
4 = Number of neutrons + 2
Number of neutrons = 4 − 2
Number of neutrons = 2
∴ The number of neutrons in a helium atom = 2.
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