Question 9
A sodium atom loses one electron and becomes an ion. What happens to its atomic number?
The right answer is the one marked above.
It does not change. The ion is still sodium.
Chemical reactions move electrons, never protons. An ion may have more or fewer electrons than protons — that is what gives it its charge — but the proton count is untouched, so the atomic number, and the element, stay exactly as they were.