The separation between a node and the next antinode is equal to one-fourth of the wavelength. Hence from the given data of the problem,
λ/4 = 25 cm = 0.25 m
→ λ= 4*0.25 m =1.0 m.
The speed of sound in air V = 340 m/s.
Hence the frequency of the vibration ν = V/λ
→ν = 340/1.0 Hz =340 Hz