#### Answer

The electron has the longer wavelength.

#### Work Step by Step

The two particles, being accelerated from rest through voltages of equal magnitude, have the same kinetic energy.
The proton has a larger mass than the electron and (if they have the same KE) will have the larger momentum because $p=\sqrt{2 m KE}$.
The wavelength is inversely proportional to the particle’s momentum, $\lambda = \frac{h}{p}$, so the proton has the shorter wavelength.