The correct option is C 3
C60 forms fcc unit cell. If N represents the number of C60 present in one unit cell, then the number of octahedral voids in one unit cell will be N and the number of tetrahedral voids in one unit cell will be 2N. Total number of voids in one unit cell will be N+2N=3N. This is equal to the number of K atoms.
Thus, for N C60 units in one unit cell , there will be 3N K atoms.
For 1 C60 unit, there will be 3 K atoms.
The formula will be K3C60=KxC60 or x=3.