GRE Physics GR 1777 Problem Solution
031. Optics and Wave Phenomena (Standing waves)
You should know about
 Standing wave in a pipe
 The frequency of the open at both ends
where n is the harmony, v is the speed of sound, L is the length of the pipe.

 The frequency of only one fixed end
Note that for the case where one end is closed, n only takes odd values just like in the case of the string fixed at only one end.

 The frequency of two closed ends
Solution
Answer
(E) None