Complete the following reaction
`RCOOH underset(Delta)overset(P_2O_5)(rarr)`?

Options

A. Acid anhydride
B. Ketone
C. Aldehyde
D. Ester

Answer

To complete the reaction of a carboxylic acid (RCOOH) with phosphorus pentoxide (P2O5), we need to understand the role of P2O5 in this reaction. P2O5 is a dehydrating agent, which means it removes water (H2O) from the reaction mixture.

### Step-by-Step Solution:

1. **Identify the Reactants**:
The reactant is a carboxylic acid, represented as RCOOH, where R is an alkyl or aryl group.

2. **Understand the Role of P2O5**:
P2O5 acts as a dehydrating agent. It removes water from the carboxylic acid, leading to the formation of an anhydride.

3. **Write the Structure of Carboxylic Acid**:
The structure of the carboxylic acid can be represented as:
\[ R-C(=O)-OH \]

4. **Dehydration Reaction**:
When P2O5 is added to RCOOH, it removes a water molecule (H2O). The hydroxyl group (-OH) from one carboxylic acid and a hydrogen atom (H) from another carboxylic acid combine to form water.

5. **Formation of Acid Anhydride**:
After the removal of water, the remaining parts of the carboxylic acids combine to form an acid anhydride. The general structure of the acid anhydride formed from two molecules of carboxylic acid is:
\[ R-C(=O)-O-C(=O)-R \]
This compound is known as an acid anhydride.

6. **Conclusion**:
The final product of the reaction is an acid anhydride, which can be represented as:
\[ R-C(=O)-O-C(=O)-R \]

### Final Answer:
The reaction of RCOOH with P2O5 leads to the formation of an acid anhydride:
\[ RCOOH \xrightarrow{P_2O_5} R-C(=O)-O-C(=O)-R \]