Assertion (A) Aldehydes and ketones, both react with Tollen's reagent to form silver mirror.
Reason (R) Both, aldehydes and ketones contain a carbonyl group.

Explanation

To solve the assertion and reason question, we will analyze both statements step by step.

### Step 1: Analyze the Assertion
The assertion states that "Aldehydes and ketones both react with Tollen's reagent to form a silver mirror."

- **Understanding Tollen's Reagent**: Tollen's reagent (Ag(NH3)2^+) is a mild oxidizing agent that is primarily used to test for aldehydes. When aldehydes are present, they reduce the silver ion to metallic silver, which forms a silver mirror on the surface of the test tube.
- **Reaction with Ketones**: Ketones do not generally react with Tollen's reagent because they are not easily oxidized. Therefore, they do not produce a silver mirror.

**Conclusion for Assertion**: The assertion is **incorrect** because only aldehydes react with Tollen's reagent to form a silver mirror, while ketones do not.

### Step 2: Analyze the Reason
The reason states that "Both aldehydes and ketones contain a carbonyl group."

- **Understanding Carbonyl Group**: Both aldehydes (RCHO) and ketones (RC(=O)R') contain a carbonyl group (C=O). This is a common feature of both classes of compounds.
- **Relevance to the Assertion**: While it is true that both contain a carbonyl group, this does not justify the assertion that both react with Tollen's reagent.

**Conclusion for Reason**: The reason is **correct** because both aldehydes and ketones do contain a carbonyl group.

### Final Conclusion
- The assertion is **incorrect**.
- The reason is **correct**.

### Answer
The correct option is **4**: Assertion is wrong, but the reason is correct.

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