Answer :
The number of neutrons in an atom can be calculated using the following formula:
Number of Neutrons = Atomic Mass (A) - Atomic Number (Z)
For the element with an atomic mass (A) of 209 and an atomic number (Z) of 83:
Number of Neutrons = 209 - 83 = 126
So, the correct answer is C. 126. This element, in this case, is bismuth (Bi), which has an atomic mass of 209 and an atomic number of 83. It has 126 neutrons. Neutrons are uncharged particles found in the nucleus of an atom, along with protons, while electrons orbit the nucleus.
To learn more about electrons, click here.
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