Which of following characteristics is not the point of resemblance between lanthanoids and actinoids?

Options

A. Reducing property.
B. Oxidation state of +3.
C. Trends of ionic radii for `M^(3+)` ions.
D. Tendency towards complex formation,

Answer

To determine which characteristic is not a point of resemblance between lanthanoids and actinoids, we need to analyze the properties of both groups of elements.

### Step-by-Step Solution:

1. **Identify Common Properties**:
- Both lanthanoids and actinoids exhibit a common oxidation state of +3. This is a significant point of resemblance as both groups predominantly form +3 oxidation states in their compounds.

2. **Reducing Properties**:
- Both lanthanoids and actinoids show reducing properties. This is due to their ability to lose electrons easily, which is another resemblance between the two series.

3. **Trends in Ionic Radii**:
- The trend of ionic radii for M³⁺ ions (where M represents the metal) is similar for both lanthanoids and actinoids. This means that as you move across the series, the ionic radii decrease in a similar manner.

4. **Tendency for Complex Formation**:
- The tendency for complex formation differs between the two groups. Actinoids generally have a higher tendency for complex formation compared to lanthanoids. This is attributed to the higher charge and smaller size of actinoid cations, which allows them to form more stable complexes.

5. **Conclusion**:
- Therefore, the characteristic that is **not** a point of resemblance between lanthanoids and actinoids is the **tendency for complex formation**.

### Final Answer:
The characteristic that is not a point of resemblance between lanthanoids and actinoids is the **tendency for complex formation**.

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