The correct option is D 4 is adjacent to 6
If 1 is adjacent to 2,3 and 5, then there is a possibility that numbers 6 or 4 has to be opposite to 1.
Hence, options A and C are definitely not possible.
The number 2 need not necessarily be adjacent to 5.
In a six-faced die, for a particular face, there is one opposite face and four adjacent faces. Therefore 4 will definitely be adjacent to 6.
Hence, option D is correct.