A hollow pipe of length 0.8 m is closed at one end. At its open end a 0.5 m long uniform string is vibrating
in its second harmonic and it resonates with the fundamental frequency of the pipe. If the tension in the wire
is 50 N and the speed of sound is 320 ms–1, the mass of the string is
(A) 5 grams (B) 10 grams
(C) 20 grams (D) 40 grams.