Calculate the frequency and wave number of a photon with a wavelength of $3.6 \ \mathring{A}$.

Given: Wavelength $(\lambda)$ = $3.6 \ \mathring{A} = 3.6 \times 10^{-10} \ m$.
Speed of light $(c)$ = $3 \times 10^{8} \ m/s$.
Frequency $(v)$ = $c / \lambda = (3 \times 10^{8} \ m/s) / (3.6 \times 10^{-10} \ m) = 8.333 \times 10^{17} \ s^{-1}$.
Wave number $(\bar{v})$ = $1 / \lambda = 1 / (3.6 \times 10^{-10} \ m) = 2.778 \times 10^{9} \ m^{-1}$.