A proton moves from south to north with a speed of \( 2 \times 10^7 \, \text{m/s} \). When a magnetic field is applied from west to east, the proton gets an acceleration of \( 10^{12} \, \text{m/s}^2 \). The mass of the proton is \( 1.6 \times 10^{-27} \, \text{kg} \). The value of the magnetic field is:

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.