Answer:
Magnetic field, B = 0.004 mT
Step-by-step explanation:
It is given that,
Charge,

Mass of charge particle,

Speed,

Acceleration,

We need to find the minimum magnetic field that would produce such an acceleration. So,

For minimum magnetic field,



B = 0.004 T
or
B = 4 mT
So, the magnetic field produce such an acceleration at 4 mT. Hence, this is the required solution.