What number of valence electrons in fluoride?
To answer this question and all other questions about valence electron, you should know where the element is on the periodic table. You can see that F is the 7th group. F is fluorine, which has 7 valence electrons. Fluoride is F with a negative charge which means it has one more electron, so Fluoride has 8 valence electrons.
Valence electrons describe the number of available electrons for bonding. The group number describes outermost electron. The elements in same group has same valence electrons. The number of electrons available for bonding are the valence electrons. In an element, the group number is equal to the number of valence electrons. So the number of electrons available for bonding can be identified by the group number.