The equation of the stationary wave is :

$\mathrm{y}=2\mathrm{Asin}\left(\frac{2\mathrm{\pi ct}}{\mathrm{\lambda }}\right)\cos \left(\frac{2\mathrm{\pi x}}{\mathrm{\lambda }}\right)$

Which of the following statements is wrong ?

Here $(2\pi \mathrm{ct}/\lambda )$ as well as. $(2\pi \mathrm{x}/\lambda )$ are dimensionless. So, unit of ct is same as that of $\lambda .$

Since, $\left[\frac{2\pi ct}{\lambda }\right]=\left[\frac{2\pi \mathrm{x}}{\lambda }\right]=\left[{\mathrm{M}}^0{\mathrm{L}}^0{\mathrm{T}}^0\right]$ 

Hence, $\frac{2\pi c}{\lambda }=\frac{2\pi x}{\lambda t}$

In the option (4) $\frac{x}{\lambda }$ is unitless. It is not the case with $\frac{c}{\lambda }$