What are the coordination numbers of li+ and s2− in the lithium sulfide crystal shown? enter the values in order of li+ and s2−, respectively?

    
As there must be twice as many lithium ions as sulphide ions, the 'numbers'
must be different. 
 It's 4:8. i.e. 4 sulphides around each lithium; and 8 lithiums around each
sulphur. 
 It's an antifluorite structure.