The frequency of electromagnetic wave, which is best suited to observe a particle of radius $$3 \times {10^{ - 4}}cm,$$   is of the order of

Solution :
Size of particle of any wave is given in terms of wavelength
$$\eqalign{ & \lambda = \frac{c}{\nu } \cr & {\text{Here,}}\,\,\lambda = 3 \times {10^{ - 4}}cm, \cr & {\text{Velocity of light in vacuum,}}\,c = 3 \times {10^{10}}cm/s \cr & \therefore 3 \times {10^{ - 4}} = \frac{{3 \times {{10}^{10}}}}{\nu } \cr & \therefore {\text{Frequency of electromagnetic wave}}\,\nu = {10^{14}}\,Hz \cr} $$