Arsenic has an atomic number of 33 and its most common isotope has a mass number of 75. How many neutrons are present in this isotope of arsenic?

• A. 33
• B. 42
• C. 108
• D. 75

Answer: (B)

Verified step by step guidance

1. Identify the atomic number of arsenic, which is given as 33. The atomic number represents the number of protons in the nucleus of the atom.
2. Note the mass number of the isotope, which is given as 75. 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: \(N = 75 - 33\), which will give the number of neutrons in the isotope.