The pair in which both actinides show +3 oxidation state only is
Ac and Lr
Actinide Oxidation States Overview
Actinides are a series of chemical elements from Actinium (Ac) to Lawrencium (Lr). They are part of the f-block elements. While many actinides show multiple oxidation states, the most common oxidation state for most actinides is +3.
However, some actinides can exhibit other oxidation states, such as +2, +4, +5, +6, and +7. The question asks for a specific pair of actinides that *only* show the +3 oxidation state among the given options.
Analyzing Specific Actinides and Their Oxidation States
Let's look at the typical oxidation states for the actinides mentioned in the options:
- Actinium (Ac): The most stable and common oxidation state is +3. It is the only known stable oxidation state for Actinium.
- Lawrencium (Lr): It is predicted and found to primarily exist in the +3 oxidation state due to its electronic configuration (\( \text{[Rn] 5f}^{14} \text{ 7s}^{2} \text{ 7p}^{1} \)), which favors the loss of three electrons. It is considered to show only the +3 state.
- Nobelium (No): While +3 is a possible oxidation state, +2 is found to be more stable in aqueous solutions. Thus, Nobelium shows both +2 and +3 oxidation states.
- Curium (Cm): The most common oxidation state is +3. However, Curium can also exhibit the +4 oxidation state, for example, in \( \text{CmF}_{4} \).
- Berkelium (Bk): Similar to Curium, Berkelium commonly exists in the +3 oxidation state but can also show the +4 oxidation state, for instance, in \( \text{BkO}_{2} \) and \( \text{BkF}_{4} \).
We can summarize the common oxidation states in a table:
| Actinide | Symbol | Common Oxidation States |
|---|---|---|
| Actinium | Ac | +3 |
| Nobelium | No | +2, +3 |
| Curium | Cm | +3, +4 |
| Berkelium | Bk | +3, +4 |
| Lawrencium | Lr | +3 |
Evaluating the Given Pairs
Now let's examine each pair provided in the options based on their oxidation states:
- Option 1: Ac and Lr
Actinium (Ac) shows only +3.
Lawrencium (Lr) shows only +3.
Both elements in this pair show only the +3 oxidation state.
- Option 2: Ac and No
Actinium (Ac) shows only +3.
Nobelium (No) shows +2 and +3.
Since Nobelium shows +2 in addition to +3, this pair does not consist of elements showing +3 only.
- Option 3: Cm and Bk
Curium (Cm) shows +3 and +4.
Berkelium (Bk) shows +3 and +4.
Both elements show +4 in addition to +3, so this pair is incorrect.
- Option 4: Cm and Lr
Curium (Cm) shows +3 and +4.
Lawrencium (Lr) shows only +3.
Since Curium shows +4, this pair is incorrect.
Conclusion
Based on the analysis of common oxidation states, the pair of actinides in which both elements show only the +3 oxidation state is Actinium (Ac) and Lawrencium (Lr).
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