Which of the following is different from others?

The equation of a simple harmonic wave is given as $y = 5 \sin \frac{\pi}{2}(100t - x)$,where $x$ and $y$ are in meters and time $t$ is in seconds. The period of the wave is: (in $s$)

$A$ transverse wave is described by the equation $y = A \sin [2\pi (f t - x/\lambda ) ]$. The maximum particle velocity is equal to four times the wave velocity if:

If the frequency of a wave is increased by $25 \%$,then the change in its wavelength is (medium not changed).

$A$ plane wave $y=a \sin (\omega t-k x)$ propagates through a stretched string. The particle velocity versus $x$ graph at $t=0$ is

Which of the following equations represents a wave?