In a row of twelve persons are facing north how many person sits between W and N? Statement I: Only two person sits between W and
X. Only one person sits between Y and X, who doesn’t sit with W. O sits third to right of M, neither of them sits adjacent to X or Y. At least two person sits between Y and N, who neither sits adjacent to O nor W, who sits at left end of the row. Only three person sits between O and Z, who doesn’t sit adjacent to Y. Statement II: X sits fourth from left end. Only two person sits between N and O. Only one person sits between W and
X. Only two person sits between Z and N, who sits immediate left of
M. O sits at end of the row

From Statement I: We have: Only two person sits between W and X. W sits at left end.  Only one person sits between Y and X, who doesn’t sit with W, that means Y sits second to right of X.  O sits third to right of M, neither of them sits adjacent to X or Y.  Only three person sits between O and Z, who doesn’t sit adjacent to Y, that means O sits at extreme right end.  At least two person sits between Y and N, who neither sits adjacent to O nor W, that means we have two different case, in case (1) N sits left of Y, in case (2) N sits right of Y. Based on above given information we have: Case-1 Clearly, only six person sits between W and N. Hence, statement II alone sufficient.