Vibrating tuning fork of frequency `n` is placed near the open end of a long cylindrical tube. The tube has a side opening and is fitted with a movable reflecting piston. As the piston is moved through `8.75 cm`, the intensity of sound changes from a maximum to minimum. If the speed of sound is `350 m//s`. Then `n` is

Vibrating tuning fork of frequency `n` is placed near the open end of a long cylindrical tube. The tube has a side opening and is fitted with a movable reflecting piston. As the piston is moved through `8.75 cm`, the intensity of sound changes from a maximum to minimum. If the speed of sound is `350 m//s`. Then `n` is

A. 500Hz
B. 1000Hz
C. 2000Hz
D. 4000Hz