Answer:
The mass number of an isotope is the sum of the number of protons and neutrons in the atomic nucleus. The atomic number is the number of protons. The calcium-40 isotope has a mass number of 40 , and an atomic number of 20 , therefore it has 20 protons.
Explanation:
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Answer:
ATOMIC STRUCTURE 3.1 - Structure of the Atom
#of protons # of neutrons # of electrons
20 40-20 = 20 20
