The correct option is A 6
Modes of vibration of air column in a closed organ pipe is given by
fn=(2n−1)v4L where n=1,2,3,4.....
Fundamental frequency f0=v4L=1500 Hz
Normal person can hear sound of frequency upto 20,000 Hz.
i.e (2n−1)=13 [odd harmonics]
Total no. of modes of vibration that can be heard by the person is 7.
(6 overtones+1 Fundamental frequency
Thus, option (c) is the correct answer.