Which has a higher frequency, a neutron or an electron? Why?

The wavelength of a particle is related by the de Broglie's equation which states that

wavelength = Planck's constant / (mass * velocity)

Given that both particles travel at the same velocity, the electron will possess a lower wavelength due to its lower mass.

This means that it will have a higher frequency because frequency and wavelength are inversely related to one another.