Question

A proton and electron have same kinetic energy. Which one has smaller de-Broglie wavelength and why ?

Answer 1

The de-Broglie wavelength in terms of kinetic energy (K) is $\lambda =\frac{h}{\sqrt{2mK}}$

For same K, $\lambda \propto \frac{1}{\sqrt{m}}$

As an electron has smaller mass then the mass of a proton so proton will have smaller wavelength.