Sure, let's work through the problem step by step.
1. Understanding the terms:
- Mass number: This is the total number of protons and neutrons in an atom's nucleus.
- Atomic number: This is the number of protons in the atom's nucleus.
- For sodium (Na), the given isotope is Na-23.
2. Given information:
- The mass number of the sodium isotope (Na-23) is 23.
- The number of neutrons in this isotope is 12.
3. Relationship between mass number, atomic number, and neutrons:
- The mass number is the sum of the protons (atomic number) and neutrons.
- Therefore, we can express this relationship as:
[tex]\[
\text{Mass number} = \text{Number of protons} + \text{Number of neutrons}
\][/tex]
4. Using the given values:
- We know the mass number (23) and the number of neutrons (12).
- Plug these values into the relationship:
[tex]\[
23 = \text{Number of protons} + 12
\][/tex]
5. Solve for the number of protons (atomic number):
[tex]\[
\text{Number of protons} = 23 - 12 = 11
\][/tex]
6. Conclusion:
- The atomic number of Na-23 is 11.
Therefore, the correct answer is:
A. 11
