If an isotope of lithium contains 5 neutrons, what is its mass number?

• A. 5
• B. 8
• C. 7
• D. 3

Answer: (B)

Verified step by step guidance

1. Recall that the mass number of an isotope is the sum of the number of protons and neutrons in its nucleus.
2. Identify the number of protons in lithium. Since lithium's atomic number is 3, it has 3 protons.
3. Note the number of neutrons given in the problem, which is 5 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: \(\text{mass number} = 3 + 5\) to find the mass number of the lithium isotope.