Question

If travelling at same speeds, which of the following will have the
shortest wavelength?

(a) Electron

(b) Neutron

(c) Proton

(d) Alpha particle

Solution

According to de- broglie relation, the species with greatest mass
will have the shortest wavelength if they are travelling at same
speeds.

 lambda = h/(mv)

Mass is inversely proportional to wavelength.

Therefore, Alpha particle being the heaviest will have the
shortest wavelength.