If two anti-nodes are observed on either side of C, the frequency of the mode in which the rod is vibrating will be (y=2×1011N/m2,  d=8×103kg/m3) length of the rod is 2.5 m

Velocity of the longitudinal waves in the rod =v=Y/d=2×1011/8000=5000 m/sThe wavelength of the wave for the mode of vibration in which 2 anti-nodes occur, is  λ=1.253/4=53mHence frequency of vibration  =n=Vλ=50005/3Hz=3000Hz