Final answer:
The correct answer is Option C. The chemical substance with the lowest magnetic moment is CrO.
Step-by-step explanation:
The chemical substance with the lowest magnetic moment is (c) CrO.
Experimental evidence of magnetic measurements supports the theory that substances with unpaired electrons are paramagnetic, meaning they are attracted to magnetic fields. While options (a) Fe₂O₃ and (b) CuO are both transition metal complexes and contain unpaired electrons, option (c) CrO contains no unpaired electrons and is therefore diamagnetic, meaning it has a slight tendency to be repelled by magnetic fields. Option (d) MnO₂ is also paramagnetic, so it is not the correct choice for the substance with the lowest magnetic moment. Therefore, the correct answer is (c) CrO.