\(9 \mathrm{~kg}\) solution is poured into a glass U-tube as shown in the figure below. The tube's inner diameter is \(2 \sqrt{\frac{\pi}{5}} \mathrm{~m}\) and the solution oscillates freely up and down about its position of equilibriwm \((x=0)\). The period of oscillation in seconds is \(\left(1 \mathrm{~m}^3\right.\) of solution has a mass \(\mu=900 \mathrm{~kg}, g=10 \mathrm{~m} / \mathrm{s}^2\), ignore frictional and swrface tension effects)

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.