To determine the isotope notation for sodium (Na) with 11 protons and 12 neutrons, follow these steps:
1. Identify the number of protons and neutrons:
Sodium has 11 protons and 12 neutrons.
2. Calculate the mass number:
The mass number of an element is the sum of its protons and neutrons.
[tex]\[
\text{Mass Number} = \text{Number of Protons} + \text{Number of Neutrons}
\][/tex]
Substituting the provided values:
[tex]\[
\text{Mass Number} = 11 + 12 = 23
\][/tex]
3. Write the isotope notation:
The isotope notation is written as the element's symbol followed by the calculated mass number. For sodium, this would be:
[tex]\[
\text{Na-23}
\][/tex]
Based on this calculation, the correct isotope notation for sodium with 11 protons and 12 neutrons is:
[tex]\[
\boxed{C. \, \text{Na-23}}
\][/tex]
