Final answer:
A sodium ion (Na+) has lost one electron compared to the neutral sodium atom, leaving it with 10 electrons. Thus, the correct answer is 10 electrons, option A.
Step-by-step explanation:
The atomic number of a sodium atom is 11, which tells us it has 11 protons. When sodium is neutral, it has the same number of electrons as protons - that includes 11 electrons.
However, when a sodium atom becomes a sodium ion (Na+), it loses one electron. This creates a positively charged ion with 11 protons and only 10 electrons. Therefore, the correct answer to how many electrons are in a sodium ion, with the symbol Na+, is 10 electrons, which corresponds to option A.