Answer:
60 cm
Step-by-step explanation:
The wavelength of the sound wave in the air column closed at one end is given by

where n = 1, 3, 5, 7,9, 11, 13, 15 are all odd numbers.
Now in our case, we know that the length of the pipe is 225 or 2.25 m. The 8th resonance corresponds to n = 15; therefore, the wavelength of the sound wave is


Hence, the wavelength of the sound wave is 60 cm.