Astatine-210 is one of the most stable isotopes of astatine. How many neutrons are present in an atom of astatine-210?

• A. 125
• B. 125
• C. 85
• D. 210

Answer: (B)

Verified step by step guidance

1. Identify the atomic number (Z) of astatine, which is the number of protons in the nucleus. For astatine, Z = 85.
2. Recognize that the isotope notation astatine-210 means the mass number (A) is 210. The mass number is the total number of protons and neutrons in the nucleus.
3. Use the relationship between mass number, protons, and neutrons: \(A = Z + N\), where \(N\) is the number of neutrons.
4. Rearrange the formula to solve for neutrons: \(N = A - Z\).
5. Substitute the known values: \(N = 210 - 85\), which gives the number of neutrons in astatine-210.