Three friends P, Q and R are wearing hats, either black or white. Each person can see the hats of the other two persons. What is the colour of P's hat? I. P says that he can see one black hat and one white hat. II. Q says that he can see one white hat and one black hat.

Considering first statement alone:
Nothing absolute can be said about the hats of Q and R, as Q might have black hat or white hat similarly R might have white or black hat as seen by P.
Considering second statement alone:
Nothing absolute can be said about the hats of P and R as they can have either Black or White caps
Even considering both statements together, we were not be able to reduce the possibilities of having black hats and white hats 
Hence answer will be D.