No of steps i.e. T(n) to move all the disks from A to C:
- Move all the disks above largest disk to B i.e. T(n-1) steps
- Then move the only disk from A to C i.e. 1 step .
- Then move remaining (n-1) disks from B to C i.e. T(n-1) steps
Adding all, T(n)=2T(n-1)+1 .
Hence B is the right answer.