How many grams of limestone with a caco3 equivalent of 100% would you need to apply to an acidic soil with 85% exchangeable al saturation to reduce it to 25%? the cec of the soil is 30 cmolc/kg.

The answer is letter c

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.