Two charged particles traverse identical helical paths in a completely opposite sense in a uniform magnetic field 
The above given case is only going to happen if both the particle experience same acceleration due to the magnetic force but opposite in direction to each other also their velocity must be same to trace the path in both senses. And, acceleration of moving charged particle due to magnetic force is given by 
where,
q is charge of particle;
v is velocity vector;
B is magnetic field vector;
m is mass of particle.
and since both the acceleration are opposite to each other so they add up to be 0. So, a1+a2=0 which simplifies to 
Hence, our answer is option (d).
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