Valence Bond Theory

- Complex ion has a 3+ charge, which causes it to have no unpaired electrons (low-spin configuration). Thus, the number of unpaired electrons is 0. This corresponds to (R). - The complex is a strong-field ligand (due to cyanide), which leads to pairing of electrons. This results in the central metal ion having 1 unpaired electron. Hence, this matches with (P). - The complex involves water as a weak-field ligand and hence has 5 unpaired electrons on the Fe^3+ ion. Therefore, this corresponds to (Q). - The complex also involves cyanide, which is a strong field ligand, and leads to the formation of 4 unpaired electrons on the central ion. This corresponds to (Q). Thus, the correct matching is: A = R, B = P, C = Q, D = Q.