A charged particle having drift velocity of
7.5×``10^{-4}`` m s-1 in an electric field of
``3×10^{-10} Vm^{-1}``, has a mobility in m2 V-1 s-1
of :
(1) 2.25×``10^{15}``
(2) 2.5×``{10^6}``
(3) 2.5×``10^{-6}``
(4) 2.25×``10^{-15}``