Scandium has an atomic number of 21 and its most abundant isotope is Sc-45. How many neutrons are present in this isotope of scandium?

• A. 24
• B. 66
• C. 21
• D. 45

Answer: (A)

Verified step by step guidance

1. Identify the atomic number of scandium, which is given as 21. The atomic number represents the number of protons in the nucleus of an atom.
2. Recognize that the isotope notation Sc-45 indicates the mass number of this isotope is 45. The mass number is the total number of protons and neutrons in the nucleus.
3. Recall the relationship between mass number (A), number of protons (Z), and number of neutrons (N): \(A = Z + N\).
4. Rearrange the formula to solve for the number of neutrons: \(N = A - Z\).
5. Substitute the known values into the equation: \(N = 45 - 21\), which will give the number of neutrons in the Sc-45 isotope.