How many neutrons are present in a neutral atom of beryllium-9?

• A. 9
• B. 4
• C. 2
• D. 5

Answer: (D)

Verified step by step guidance

1. Identify the atomic number (Z) of beryllium, which is the number of protons. For beryllium, Z = 4.
2. Recognize that the mass number (A) of the isotope is given as 9 in beryllium-9. The mass number represents the total number of protons and neutrons in the nucleus.
3. Recall that the number of neutrons (N) can be found by subtracting the atomic number from the mass number: \(N = A - Z\).
4. Substitute the known values into the formula: \(N = 9 - 4\).
5. Calculate the difference to find the number of neutrons in beryllium-9.