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

According to de-Broglie equation,

$\mathrm{\lambda }=\frac{\mathrm{h}}{\mathrm{mv}}$

For the same speed of different particles, this implies v is constant and h is also constant.

$\mathrm{\lambda }\infty \frac{1}{\mathrm{m}}$

Higher is the mass of matter waves, lesser is the wavelength, and vice-versa. In these matter waves, an alpha particle (He²⁺) has a higher mass, and therefore has the shortest wavelength.