Which of the following is the mass number of the most common isotope of boron?

• A. 11
• B. 15
• C. 10
• D. 5

Answer: (A)

Verified step by step guidance

1. Understand that the mass number of an isotope is the total number of protons and neutrons in its nucleus.
2. Recall that boron has an atomic number of 5, which means it has 5 protons.
3. Identify the most common isotope of boron by considering the typical number of neutrons it contains; the most common isotope has 6 neutrons.
4. Calculate the mass number by adding the number of protons and neutrons: \(\text{mass number} = \text{protons} + \text{neutrons}\).
5. Substitute the values for boron: \(\text{mass number} = 5 + 6\) to find the mass number of the most common isotope.