An ion, MII, forms the complexes [M(H2O)6]2+, [MBr6]4–, and [M(en)3]2+. The colors of the complexes, though not necessarily in order, are green, red, and blue. Match the complex with the appropriate color, and explain.

We know that varying strengths of complexes as some have greater pairing energy whereas others have more splitting energy.In the given complexes en is stronger complex followed by H2O and then Br.

Since red has the least energy it will be corresponding to en complex, green will be shown by water complex and blue will be shown by bromine complex.