Chlorine has an atomic number of 17 and contains 18 neutrons. What is its mass number?

• A. 17
• B. 35
• C. 34
• D. 18

Answer: (B)

Verified step by step guidance

1. Recall that the mass number of an atom is the total number of protons and neutrons in its nucleus.
2. Identify the number of protons, which is equal to the atomic number. For chlorine, the atomic number is 17, so it has 17 protons.
3. Identify the number of neutrons given in the problem, which is 18 for chlorine.
4. Use the formula for mass number: \(\text{Mass Number} = \text{Number of Protons} + \text{Number of Neutrons}\).
5. Substitute the values: \(\text{Mass Number} = 17 + 18\) to find the mass number of chlorine.