Is mobility scalar or vector quantity?

Dear Student,
Drift velocity in a material is directly proportional to electric field intensity. Mobility is a constant of proportionality and is a scalar quantity.  It is defined as drift velocity per unit electric field. 
$$\begin{gathered} \overrightarrow{v_d}=\mu \overrightarrow{E} \\ So, \\ \mu =\frac{\overrightarrow{v_d}}{\overrightarrow{E}} \end{gathered}$$
Regards