Question #c451f

As explained in above figure that in the resonance air column experiment with one end closed tube we get first resonance air column at the length $\frac{\lambda}{4}$ , where $\lambda$ is the wave length of sound wave produced by the tuning fork in use. Here the length of 1st resonant air column is ${l}_{1} = 15 c m$.
Hence $l a m \frac{\mathrm{da}}{4} = 15 c m$
${l}_{2} = \frac{3 \lambda}{4} = 3 \times 15 = 45 c m \to \text{option(c)}$