Case Study Question 1 on d & f Block – Chapter 8 CBSE Class 12 Chemistry

Case Study Question on d & f Block

Read the passage given below and answer the following questions:

Within the 3d series, manganese exhibits oxidation states in aqueous solution from +2 to +7, ranging from Mn²⁺(aq) to MnO⁻₄ (aq). Likewise, iron forms both Fe²⁺(aq) and Fe³⁺(aq) as well as the FeO²⁻₄ ion. Cr and Mn form oxyions CrO²⁻₄ , MnO⁻₄ , owing to their willingness to form multiple bonds . The pattern with the early transition metals—in the 3d series up to Mn, and for the 4d, 5d metals up to Ru and Os—is that the maximum oxidation state corresponds to the number of ‘‘outer shell’’ electrons. The highest oxidation states of the 3d metals may depend upon complex formation (e.g., the stabilization of Co³⁺ by ammonia) or upon the pH (thus MnO ²⁻ (aq) is prone to disproportionation in acidic solution). Within the 3d series, there is considerable variation in relative stability of oxidation states, sometimes on moving from one metal to a neighbor; thus, for iron, Fe³⁺ is more stable than Fe²⁺, especially in alkaline conditions, while the reverse is true for cobalt. The ability of transition metals to exhibit a wide range of oxidation states is marked with metals such as vanadium, where the standard potentials can be rather small, making a switch between states relatively easy.

(Cotton, S. A. (2011). Lanthanides: Comparison to 3d metals. Encyclopedia of inorganic and Bioinorganic Chemistry.)

In the following questions, a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices on the basis of the above passage.

A. Assertion and reason both are correct statements and reason is correct explanation for assertion.

B. Assertion and reason both are correct statements but reason is not correct explanation for assertion.

C. Assertion is correct statement but reason is wrong statement.

D. Assertion is wrong statement but reason is correct statement.

1. Assertion: Highest oxidation state is exhibited by transition metal lying in the middle of the series.

Reason: The highest oxidation state exhibited corresponds to number of (n-1)d electrons.

2. Assertion: Fe³⁺ is more stable than Fe²⁺

Reason: Fe³⁺ has 3d⁵ configuration while Fe²⁺ has 3d⁶ configuration.

3. Assertion: Vanadium had the ability to exhibit a wide range of oxidation states.

Reason: The standard potentials Vanadium are rather small, making a switch between oxidation states relatively easy.

4. Assertion: Transition metals like Fe, Cr and Mn form oxyions

Reason: Oxygen is highly electronegative and has a tendency to form multiple bonds.

5. Assertion: The highest oxidation states of the 3d metals depends only on electronic configuration of the metal.

Reason: The number of electrons in the (n-1)d and ns subshells determine the oxidation states exhibited by the metal.

Ans: 1 c, 2 a, 3 a, 4 b, 5d