(d) On comparing the given equation with standard equation $y = a\sin{\frac{2\pi}{\lambda}(vt - x)}.$ It is clear that wave speed $(v)_{wave} = v$ and maximum particle velocity $\left( v_{\max} \right)_{particle} = a\omega = y_{0} \times$ co-efficient of $t = y_{0} \times \frac{2\pi v}{\lambda}$
$\because\left( v_{\max} \right)_{particle} = 2(\omega)_{wave} \Rightarrow \frac{a \times 2\pi v}{\lambda} = 2v \Rightarrow \lambda = \pi y_{0}$