The magnetic flux near the axis and inside the air core solenoid of length 80 cm carrying current ' I ' is \(1.57 \times 10^{-6} \mathrm{~Wb}\). Its magnetic moment will be [cross-sectional area of a solenoid is very small as compared to its length,\(\mu_0=4 \pi \times 10^{-7} \text { SI unit] }(\pi=3.14)\)

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.