The correct option is A 5me×10−5 seconds where m is the mass of the electrons and e is the charge
From the videos you would have seen that,
Vd=eEτm, where τ =Average time between successive collisions also called relaxation time.
Now you just need to plug in the values.
5×10−4=10eτ/m
τ=5me×10−5seconds.
You can use dimensional analysis to eliminate some options. Sometimes this method can be very useful.