When a sound wave of wavelength $'\lambda'$ is propagating in a medium, the maximum velocity of the particle is equal to the wave velocity. The amplitude of wave is

Question

$$\begin {array} {1 1} (1)\;\lambda & \quad (2)\;\frac{\lambda}{2} \\ (3)\;\frac{\lambda}{2 \pi} & \quad (4)\;\frac{\lambda}{4 \pi} \end {array}$$