Assertion (A): Lithium reacts with oxygen to form `Li_(2)O`, but potassium reacts with oxygen to form `KO_(2)`.
Reason (R ): Potassium is more reactive than lithium.

Options

A. If both (A) and (R ) are correct and (R ) is the correct explanation of (A).
B. If both (A) and (R ) are correct, but (R ) is not the correct explanation of (A).
C. If (A) is correct, but (R ) is incorrect.
D. If (A) is incorrect, but (R ) is correct.

Explanation

To analyze the given question, we need to evaluate both the assertion and the reason provided.

### Step 1: Evaluate the Assertion
The assertion states that lithium reacts with oxygen to form `Li2O`, while potassium reacts with oxygen to form `KO2`.

- **Lithium Reaction**: Lithium reacts with oxygen to form lithium oxide (`Li2O`). This is a well-known reaction where lithium, being a smaller alkali metal, forms a normal oxide.

- **Potassium Reaction**: Potassium, on the other hand, reacts with oxygen to form potassium superoxide (`KO2`). This occurs because potassium is larger and has a weaker positive field, allowing it to stabilize the superoxide ion.

**Conclusion for Assertion**: The assertion is correct.

### Step 2: Evaluate the Reason
The reason states that potassium is more reactive than lithium.

- **Reactivity of Alkali Metals**: The reactivity of alkali metals increases down the group in the periodic table. Potassium, being lower in the group than lithium, is indeed more reactive. This increased reactivity is due to potassium's larger atomic size, which results in a lower ionization energy, allowing it to lose its outermost electron more easily than lithium.

**Conclusion for Reason**: The reason is also correct.

### Step 3: Determine the Relationship Between Assertion and Reason
Now we need to determine if the reason provided is a correct explanation for the assertion.

- While both statements are correct, the reason (potassium being more reactive than lithium) does not directly explain why lithium forms `Li2O` and potassium forms `KO2`. The formation of different oxides is more related to the size and charge density of the metal cations rather than just their reactivity.

### Final Conclusion
- Both the assertion and the reason are correct, but the reason does not serve as a correct explanation for the assertion.

Thus, the correct option is:
**Option B**: Both Assertion and Reason are correct, but Reason is not the correct explanation of Assertion.

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