Thank you for reporting, we will resolve it shortly
Q.
The de-Broglie wavelength of a particle of kinetic energy ' $K$ ' is $\lambda$; the wavelength of the particle, if its kinetic energy is $\frac{K}{4}$ is
$\lambda \propto \frac{1}{\sqrt{ k }}$
$\frac{\lambda_{1}}{\lambda_{2}}=\sqrt{\frac{ k _{2}}{ k _{1}}},=\sqrt{\frac{ k }{4 k }}=\frac{1}{2}$
$\lambda_{2}=2 \lambda$