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Answer: A mass number is the sum of protons and neutrons in a nucleus. It is different from the atomic number as it only shows the number of protons in an atom’s nucleus.
The mass number of an element is calculated by adding the atomic number of that element with the number of neutrons in that element.
A = Z+N
Where A = mass number, Z = atomic number, and N = Number of neutrons.
Oxygen has an atomic number: of 8
Oxygen has 3 isotopes with 8, 9, and 10 neutrons in the first, second and third isotopes.
So the Mass number for:
- First Isotope = 8 + 8 = 16
- Second Isotope = 8 + 9 = 17
- Third Isotope = 8 + 10 = 18
The mass number of oxygen for its first, second and third Isotope is 16, 17, and 18, respectively.
