* Atomic Number: Sodium (Na) has an atomic number of 11. This means a neutral sodium atom always has 11 protons.
* Neutrality: A neutral atom has an equal number of protons and electrons.
* Isotopes: The "25" in sodium-25 refers to its mass number, which is the total number of protons and neutrons. It doesn't change the number of electrons in a neutral atom.
Therefore, a neutral atom of sodium-25 has 11 electrons.
