Fluorite(CaF2) adopts face centred cubic structure with latice parametre a=5.463 unit,.lf the ionic radius of anion(F-) is is 1.71 unit,the ionic radius of cation(Ca 2+) is unit.(in 2decimal places)
This same question came in gate 2017 and I think the structure you might have seen of CaF2 in books or anywhere else will lead to other answer quite different from what given in ga...