Explanation :
The energy of an electron in the n=2 energy level can be calculated using the energy equation for hydrogen atoms:
E = -13.6 eV/n²
where E is the energy in electron volts (eV) and n is the principal quantum number. Converting the energy given in the problem from joules to electron volts:
-21.8 x 10^(-19) J = -21.8 x 10^(-19) J x (6.242 x 10^18 eV/J) ≈ -136.1 eV
Plugging in n=2 into the energy equation:
E = -13.6 eV/2²
E = -13.6 eV/4
E ≈ -3.4 eV
Therefore, the energy of the n=2 energy level is approximately -3.4 eV.
When an electron jumps down from n=2 to n=1, it emits a photon with energy equal to the difference in energy between the two energy levels. Using the energy values calculated above:
∆E = (-3.4 eV) - (-136.1 eV)
∆E = 132.7 eV
The energy of the photon emitted is approximately 132.7 electron volts (eV).