The diagram shows two tubes. [Figure showing two tubes, X and Y. Tube X is closed at the bottom, open at the top. Tube Y is open at both ends.] The tubes are identical except tube X is closed at its lower end while tube Y is open at its lower end. Both tubes have open upper ends. A tuning fork placed above tube X causes resonance of the air at frequency f. No resonance is found at any lower frequency than f with tube X. Which tuning fork will produce resonance when placed just above tube Y?

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.