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

From I: We have: Only two person sits between Z and R. Z sits at left end. Only one person sits between W and R, who doesn’t sit with Z, that means W sits second to right of R.  D sits third to right of M, neither of them sits adjacent to R or W.  Only three person sits between D and H, who doesn’t sit adjacent to W, that means D sits at extreme right end.   At least two person sits between W and O, who neither sits adjacent to D nor Z, that means we have two different case, in case (1) O sits left of W, in case (2) O sits right of W. Based on above given information we have: case-1 Hence, statement I is not sufficient. From II: We have: R sits fourth from left end.  Only one person sits between Z and R, that means we have two possible place for Z, in case (1) Z sits second to left of R, in case (2) Z sits second to right of R.  Only two person sits between O and D. D sits at end of the row. Only two person sits between H and O, who sits immediate left of M, that means D sits at extreme right end and case (2) is not valid. Based on above given information we have: Clearly, only six person sits between Z and O. Hence, statement II alone sufficient