The frequency of e.m. wave which is best suited to observe a particle of radius 3×10−4 cm, is of the order of

Radius of particle is λ. ∴ v=cλ=3×1086×10−6=5×1013 Hz. So the order of magnitude is 1014For observation of particle, the wave frequency should be more than 1014 Hz, or wavelength should be smaller.