Correct Answer - Option 2 : λ = πy
0/2
\(\begin{array}{l} v\; = \;\frac{{dy}}{{dt}}\; = \;{y_0}2\pi f\cos 2\pi (ft - \frac{x}{{{\rm{\lambda \;}}}})\\ {v_{max}}\; = \;{y_0}2\pi f \end{array}\)
Wave velocity: \(v\; = \;f\lambda\)
Given: \({v_{max}}\; = \;4v \Rightarrow {y_0}2\pi f\; = \;4f\lambda \Rightarrow \lambda \; = \;\frac{{{y_0}\pi }}{2}\)