Fluorine has 9 electrons because its atomic number is 9, which means it has 9 protons in its nucleus. In a neutral atom, the number of electrons is equal to the number of protons. Therefore, a neutral fluorine atom has 9 electrons.
When fluorine has a charge of 1 (F–), it means it has gained one extra electron. This results in a total of 10 electrons. The charge of an ion is determined by the difference between the number of protons and electrons. In the case of F–, the extra electron gives it a negative charge of 1.
So, the number of electrons in a neutral fluorine atom is equal to its atomic number (9), but when it gains an electron to form F–, it has 10 electrons.