(b) The first overtone may be 400 Hz.
(c) The first overtone may be 600 Hz.
(d) 600 Hz is an overtone.
For an open organ pipe:
nth harmonic = (n – 1)th overtone
If the pipe is an open organ pipe, then the 1st overtone is 400 Hz. Option (b) is correct.
Also, υ3 = 600 Hz, i.e., second overtone = 600 Hz.
600 Hz is an overtone. Therefore, option (d) is correct.
If the pipe is a closed organ pipe, then .
(2n – 1)th harmonic = (n – 1)th overtone
For n = 2:
1st overtone = 3rd harmonic = 3υ1
=3 × 200
= 600 Hz
Therefore, option (c) is also correct.