NaCl has fcc structure becoz in NaCl ,Cl anions are present at all the eight corners and at all the six faces.

contribution due to Corner particles is 1/8X8=1

contribution due to face particles is 1/2X6=3

there fore total is equal 4 Cl anions

and Na cations are present at the body centre and centre of all the 12 edges

contribution due to body centre particle =1

contribution due to edge particle =1/4X12=3

total is equal to 4 Na cations

becoz of anionic arrangement it is called at fcc.