Ammonium sulfate was added to red urine. The urine had a positive reaction for blood, but no RBCs were seen on microscopic examination. After centrifugation the supernatant fluid is red. The abnormal color is caused by .

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.