Then I believe the professor may be wrong in his terms. Regardless, if that may be the condition as how BluePill said, then which of the two is paramagnetic and diamagnetic? I was able to find out more about the question. It would seem that only one of the compounds given would decrease in weight and the other increase. I am confused about the question myself but I would only like to understand how the principle of changing a weight of a compound in a magnetic field works.

If we take K_{4}Fe(CN)_{6}, taking the oxidation state of iron it would be +2 since CN_{6} would be -6 and the four K^{+} would be equal to +4. Taking iron, its configuration would have a [Ar]3d^{6}. Is it correct to say that this is diamagnetic, following crystal field theory? It is diamagnetic since cyanide is a strong-field ligand and would tend to have the electron spins at the low-spin complex. I'm not sure at my explanation though. How could I then explain how the weights change?

If it is diamagnetic, then what can I assume about its weight?

I may have gotten this wrong, please tell me if I followed correctly. Thank you.