The second overtone of an open organ pipe has the same frequency as the first overtone of a closed pipe  L metre long. The length of the open pipe will be

Second overtone of an open organ pipe = Third harmonic =3×v0'=3×v2L'First overtone of a closed organ pipe= Third harmonic =3×v0=3×v4LAccording to question3v0'=3v0⇒3×v2L'=3×v4L⇒L'=2L