An isotope of sodium (Na) has a mass number of 22. How many neutrons does it have?

• A. 12
• B. 13
• C. 11
• D. 10

Answer: (A)

Verified step by step guidance

1. Identify the mass number of the sodium isotope, which is given as 22.
2. Recall that the mass number of an isotope is the sum of its protons and neutrons.
3. Determine the atomic number of sodium (Na) from the periodic table, which is 11. This represents the number of protons in the sodium atom.
4. Use the formula: \( \text{Number of neutrons} = \text{Mass number} - \text{Atomic number} \).
5. Substitute the known values into the formula: \( \text{Number of neutrons} = 22 - 11 \).