In to a vessel containing pure water a clean glass tube of radius \(3.6 \times 10^{-4} \mathrm{~m}\) is held vertically with 12 cm of the tube above the water level. Now the capillary tube is moved down in to the water so that only 2 cm of its length is above the water surface. Angle of contact \(\theta\) at this position is (given surface tension of water \(=7.2 \times 10^{-2} \mathrm{Nm}^{-1}\) and \(g=10 \mathrm{~ms}^{-2}\))

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.