Let $\overrightarrow{\mathrm{A}}$ be  a unit vector along the axis of rotation of a purely rotating body and $\overrightarrow{\mathrm{B}}$ be a unit vector along the velocity of a particle P of the body away from the axis. The value of $\overrightarrow{\mathrm{A}}.\stackrel{\rightharpoonup }{\mathrm{B}}$ is
 

A and B are orthogonal to each other since they are perpendicular to the axis of rotation and to the velocity of the particle, respectively.

As $\overrightarrow{\mathrm{A}}$ and $\overrightarrow{\mathrm{B}}$ are perpendicular thus,

$\overrightarrow{\mathrm{A}}.\stackrel{\rightharpoonup }{\mathrm{B}}=0$

Hence the correct answer is zero.