The value of Planck’s constant is $$6.63 \times {10^{ - 34}}Js.$$   The speed of light is $$3 \times {10^{17}}nm\,{s^{ - 1}}.$$   Which value is closest to the wavelength in nanometer of a quantum of light with frequency $$6 \times {10^{15}}{s^{ - 1}}?$$

Solution :
$$\eqalign{ & {\text{Given, Planck's constant,}} \cr & h = 6.63 \times {10^{ - 34}}Js \cr & {\text{Speed of light,}}\,\,c = 3 \times {10^{17}}nm\,{s^{ - 1}} \cr & {\text{Frequency of quantam light}} \cr & \nu = 6 \times {10^{15}}{s^{ - 1}} \cr & {\text{Wavelength,}}\,\,\,\lambda = ? \cr & {\text{We know that,}}\,\,\,\nu = \frac{c}{\lambda } \cr & {\text{or,}}\,\,\lambda = \frac{c}{\nu } \cr & \,\,\,\,\,\,\,\,\,\,\,\,\, = \frac{{3 \times {{10}^{17}}}}{{6 \times {{10}^{15}}}} \cr & \,\,\,\,\,\,\,\,\,\,\,\,\, = 0.5 \times {10^2}\,nm \cr & \,\,\,\,\,\,\,\,\,\,\,\,\, = 50\,nm \cr} $$