What is the wavelength of light absorbed by [co(nh3)6]3+? a. greater than 7.70×10^2 nm b. less than 2.90×10^2 nm c. between 2.90×10^2 nm and 7.70×10^2 nm

The problem here is that according to aufbau principle before 3d orbital 4s subshell comes.after filling 3p orbital with electrons you have 4 electrons left, you place two in 4s with opposite spin and the other two in 3d in any of its two orbitals of total five orbitals with the same spin.