when a proton is released from rest, intitially it is accelerated twowards west direction due to electric field which is acting westwards
( in west direction ) ..............................(1)
when the proton is projected in North direction with velocity v0 , proton is subjected to electric field and magnetic field.
Proton is moving towards west with acceleration 3a0 . Since force is acting in west direction and its velocity is towards north ,
magnetic field is acting downward direction ( see figure )
since it is known that electric field gives an acceleration ao , additional acceleration 2ao is given by magnetic field
( downward direction )
Hence in the list of options given in the answer, (b) is the correct one