Explanation:
From the atomic emission spectrum of Mercury, the wavelength of the dark green line is 545 nm.
The relation between the frequency and wavelength is given by :
[tex]c=f\times \lambda[/tex]
[tex]f=\dfrac{c}{\lambda}[/tex]
[tex]f=\dfrac{3\times 10^8\ m/s}{545\times 10^{-9}\ m}[/tex]
[tex]f=5.504\times 10^{14}\ Hz[/tex]
Let E is the energy of an dark green photon emitted by the mercury atom. It is given by :
[tex]E=hf[/tex]
h is Planck's constant
[tex]E=6.63\times 10^{-34}\ J-s\times 5.504\times 10^{14}\ Hz[/tex]
[tex]E=3.64\times 10^{-19}\ J[/tex]
Hence, this is the required solution.