There are four different isomers for C3H6O2 that satisfy the given conditions:

1. Methyl ethanoate or methyl acetate

- Molecular formula: CH3COOCH3
- Structure: CH3COOCH3
- Reduces Tollens reagent
- Forms C5H8O3 on treatment with acetic anhydride

2. Ethyl methanoate or ethyl formate

- Molecular formula: CH3COOCH2CH3
- Structure: CH3COOCH2CH3
- Reduces Tollens reagent
- Forms C5H8O3 on treatment with acetic anhydride

3. Propanoic acid

- Molecular formula: CH3CH2COOH
- Structure: CH3CH2COOH
- Reduces Tollens reagent
- Forms C5H8O3 on treatment with acetic anhydride

4. Lactic acid

- Molecular formula: CH3CH(OH)COOH
- Structure: CH3CH(OH)COOH
- Reduces Tollens reagent
- Forms C5H8O3 on treatment with acetic anhydride

Explanation:

Isomers are molecules with the same molecular formula but different structural formulas. C3H6O2 has several possible isomers, but only four of them satisfy the given conditions.

Tollens reagent is a solution of silver nitrate and ammonia used to test for the presence of aldehydes. Aldehydes are oxidized by Tollens reagent, reducing the silver ions to metallic silver.

Acetic anhydride is a reagent commonly used to convert carboxylic acids to esters. When a carboxylic acid is treated with acetic anhydride, an ester is formed along with acetic acid.

The four isomers listed above are the only ones that satisfy both conditions. Other isomers may reduce Tollens reagent or form an ester with acetic anhydride, but not both.