Choose the correct relation if the wavelength $\lambda$, frequency f and velocity v of

The frequency is the number of times a cycle is completed in a second. The time it takes for one vibration to complete is referred to as the time period. The number of vibrations each second is frequency, which is inversely related to time period.

We know that formula of time periode, T=1/f

Here, f is the frequency, T is time period
We know that Speed = Distance / Time taken
Speed of wave is it's velocity v, and Distance of wave is it's wavelength $\lambda$.
Substituting these into the equation.
$\Rightarrow v=\lambda T$
$\Rightarrow v=\lambda f$
As, T=1 / f
Thus, $\mathbf{v}=\mathbf{f} \lambda$