Question

Which of the following arrangements does not represent the correct order of properties stated against it?
(A). V2+ < Cr2+ < Mn2+ < Fe2+: Paramagnetic behavior
(B). Zn2+ < Ni2+ < Cr2+ < Fe2+: Number of unpaired electrons
(C). Sc3+ < Ti3+ < V3+ < Cr3+ < Mn3+: Number of oxidation states
(D). Co2+ < Cr2+ < Mn2+ < Ni2+: Stability in aqueous solution
Choose the correct answer from the options given below:

• A. (A), (B) and (C) only
• B. (A) and (C) only
• C. (A), (B) and (D)
• D. (B), (C) and (D) only

Hint:

The number of unpaired electrons dictates the paramagnetic behavior, but it should not be interpreted without taking into account the experimental conditions as well as ligand field effects.

Answer 1

The Correct Option is C

Here’s an analysis of the given properties for the arrangements:
(A) Paramagnetic Behavior: Paramagnetism is due to unpaired electrons. The expected order would follow the number of unpaired electrons. Fe2+ with four unpaired electrons should be more paramagnetic than Mn2+ and less paramagnetic than Cr2+. The given order is incorrect.
(B) Number of Unpaired Electrons: The number of unpaired electrons for the transition metal cations in the given list does not follow a regular increasing pattern. For example, Cr2+ will have 4 unpaired electrons whereas Ni2+ will have 2 unpaired electrons. Zn2+ is diamagnetic. Thus this order is incorrect.
(C) Number of Oxidation States: Transition metals exhibit a variety of oxidation states, where the lower the number of d electrons the lesser the oxidation states will be. Sc3+ can exist as Sc3+. The stability increases from Ti3+ to Mn3+. Therefore, the given order is correct.
(D) Stability in Aqueous Solution: The stability of transition metal ions in aqueous solution is influenced by several factors like the charge density, hydration energy and crystal field stabilization energy. Stability order is not consistent and is based on these factors and is highly complex and does not follow a general trend. The given order is not correct.