The chemical combination of two or more substances which can only be seperated by chemical means its called

Chemical reaction or an extraction

Chemical Compound or extraction

The answer is c) pyrite

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.