Correct Answer - A
The figure shows variation of displacement of particles in a closed organ pipe for `3^(rd)` overtone.
For third overtone `l=(7lamda)/(4)` or `lamda=(4last)/(7)` or `(lamda)/(4)=(l)/(7)`
Hence the amplitude at P at a distance `(l)/(7)` from closed end is `a` because there is an antinode at that point.