Final answer:
The excitation energy can be calculated using the formula E_n = (n^2 * h^2) / (8 * m * L^2).
Step-by-step explanation:
The excitation energy from the ground level to the third excited level for an electron confined to a box with a width of 0.125 nm can be calculated using the formula:
E_n = (n^2 * h^2) / (8 * m * L^2)
Where E_n is the energy level, n is the quantum number of the energy level, h is the Planck's constant (6.626 x 10^-34 J*s), m is the mass of the electron (9.109 x 10^-31 kg), and L is the width of the box.
To find the excitation energy from the ground level to the third excited level, we can subtract the energy of the ground level from the energy of the third excited level:
Excitation Energy = E_3 - E_1