Final answer:
Different isotopes of sodium are represented by the notations 22Na and 23Na, corresponding to the mass numbers of each isotope, with both having 11 protons and differing neutron counts.
Step-by-step explanation:
The notations which represent different isotopes of the element sodium are given by (4) 22Na and 23Na. These notations include a number and the symbol for sodium (Na). The number represents the isotope's mass number, which is the sum of the number of protons and neutrons in the nucleus. Sodium, with the standard notation 22Na, has 11 protons, 12 neutrons, and 11 electrons. Another isotope, sodium-23 or 23Na, would still have 11 protons (since the atomic number of sodium is 11 and defines the element) but would have 12 neutrons. Isotopes of an element have the same number of protons but different numbers of neutrons, which gives them different mass numbers.