(A)→(P), (T) For a pipe closed at one end, we have
4λf​​ = L or
λf​ = 4L
Therefore, the sound waves are longitudinal.
(B)→(P), (S) For a pipe open at both ends, we have
2λf​​ = L or
λf​ = 2L
Therefore, the sound waves are longitudinal.
(C)→(Q), (S) For a stretched wire clamped at both ends, we have
λf​/2 = L
Vibration on the string is transverse.
(D)→(Q), (R) For a stretched wire clamped at both ends and at mid-point, we have
2λf​​ =
2L​ ⇒
λf​ = L
Therefore, the vibration on the string is transverse.