A cylinderical tube, open at one end and closed at the other, is in acoustic unison (resonance) with an external source of sound of singal frequency held at the open end of the tube, in its fundamental note.
Then :

Options

A. the displacement wave from the source gets reflected with a phase change of `pi` at the closed end
B. the pressrue wave from the source get reflected without a phase change at the closed end
C. the wave reflected from the closed and again gets reflected at the open end
D. the wave reflected from the closed end does not suffer reflection at the open end

Answer

A, B, C

Explanation

When sound wave is reflected from rigid end displacement wave get extras phase at `pi` and pressure wave get no extra phase
So option `A, B, C` are correct.