Question

The correct statements among the following are:
A. Mo(VI) and W(VI) are less stable than Cr(VI).
B. Ce⁴⁺ and Tb⁴⁺ are oxidant while Eu²⁺ and Yb²⁺ are reductant.
C. Cm and Am have seven unpaired electrons.
D. Actinoid contraction is greater from element to element than lanthanoid contraction.
Choose the correct answer:

• A. A and B Only
• B. C and D Only
• C. B and D Only
• D. A and C Only

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
We evaluate the individual inorganic chemistry statements regarding d-block group stability trends, lanthanide redox properties, actinide electron configurations, and periodic contraction effects.
Step 2: Key Formula or Approach:
- Heavy d-block elements favor higher oxidation states compared to their lighter group members.
- Lanthanides strongly favor the +3 oxidation state. Deviations (+2 or +4) will act to gain or lose electrons to return to +3.
- 5f electrons shield the nucleus poorly, worse than 4f electrons.
Step 3: Detailed Explanation:
Statement A:
In the d-block, the stability of higher oxidation states generally *increases* down a group. Therefore, \(\text{Mo}(\text{VI})\) and \(\text{W}(\text{VI})\) are actually *more* stable than \(\text{Cr}(\text{VI})\). (\(\text{Cr}(\text{VI})\) in dichromate is a strong oxidizing agent, meaning it prefers to reduce, whereas \(\text{WO}_3\) is very stable). So, Statement A is False.
Statement B:
The most stable oxidation state for lanthanides is +3.
\(\text{Ce}^{4+}\) and \(\text{Tb}^{4+}\) tend to gain an electron to become +3. Gaining electrons makes them oxidizing agents (oxidants).
\(\text{Eu}^{2+}\) and \(\text{Yb}^{2+}\) tend to lose an electron to become +3. Losing electrons makes them reducing agents (reductants).
So, Statement B is True.
Statement C:
Americium (\(\text{Am}\), \(Z=95\)): electronic configuration is \([\text{Rn}] 5f^7 7s^2\). It has 7 unpaired electrons in the 5f subshell.
Curium (\(\text{Cm}\), \(Z=96\)): electronic configuration is \([\text{Rn}] 5f^7 6d^1 7s^2\). It has 7 unpaired electrons in 5f AND 1 unpaired electron in 6d, yielding a total of 8 unpaired electrons.
So, Statement C is False.
Statement D:
Actinoid contraction is indeed greater from element to element than lanthanoid contraction. This is because the 5f electrons provide even poorer shielding from the increasing nuclear charge than the 4f electrons do.
So, Statement D is True.
Step 4: Final Answer:
The correct statements are B and D only.