Answer:
A-210, n-125
A-207, n-122
A-209, n-124
Explanation:
The mass number is the sum of the number of protons and neutrons in the nucleus of an atom.
Astatine has an atomic number of 85, this is the number of protons in its nucleus. We must subtract the given number of neutrons in each option from the mass number and consider the difference. If the difference between the mass number and number of neutrons is exactly 85, then that option represents one of the isotopes of astatine.
