Question

Why are there two fluoride ions in magnesium fluoride but only one fluoride ion in lithium fluoride

Answer 1

Answer:

Idk

Explanation:

Answer 2

This would be more of a chemistry question. Remember magnesium has a charge of 2+, and would need to hand off its two extra electrons. Fluorine can only take one electron at a time, so there needs to be two fluorines to take one magnesium's 2 electrons. 

With lithium, it has a +1 charge, so it has one extra electron, which it can hand off to just 1 fluorine atom. 

Another way of looking at this is: $Mg^{2+}$ + 2$F^{-}$ = MgF2  (the charges must balance out to zero)

$Li^{+}$ + $F^{-}$ = LiF (the charges balance out to zero)