A Substance $A_xB_y$ crystallizes in a face centered cubic (FCC) lattice in which 'A' atoms occupy each corner of the cube and 'B' atoms occupy the centers of each face of the cube , Identify the correct composition of the substance $A_xB_y$

Question

$\begin{array}{1 1} AB_3 \\ A_4B_3 \\ A_3B \\ Composition \;cannot \;be \;specified \end{array}$