In the Cannizzaro reaction given below:
`2Ph-CHO overset(overset(Θ)OH)rarrPh-CH_(2)OH+PhCO_(2)^(-)` the slowest step is:

Options

A. The attack of `OH^(-)` at the carbonyl group
B. The transfer of hydride to the carbonyl group
C. The abstraction of proton from the carboxylic group
D. The deprotonation of pH -`CH_(2)OH`

Answer

To determine the slowest step in the Cannizzaro reaction, we will analyze the mechanism of the reaction step by step.

### Step-by-Step Solution:

1. **Identify the Reaction**: The Cannizzaro reaction involves the disproportionation of aldehydes that lack alpha hydrogens in the presence of a strong base (like OH⁻). The reaction can be represented as:
\[ 2 \text{Ph-CHO} \xrightarrow{\text{OH}^-} \text{Ph-CH}_2\text{OH} + \text{PhCO}_2^- \]

2. **Mechanism Overview**: The mechanism consists of several steps:
- **Step 1**: Nucleophilic attack by hydroxide ion (OH⁻) on the carbonyl carbon of the aldehyde (Ph-CHO), forming a tetrahedral intermediate.
- **Step 2**: Transfer of a hydride ion (H⁻) from one aldehyde molecule to the carbonyl carbon of another aldehyde molecule.
- **Step 3**: Proton abstraction from the intermediate to form benzyl alcohol (Ph-CH₂OH) and benzoate ion (PhCO₂⁻).

3. **Step 1 - Nucleophilic Attack**: In this step, the hydroxide ion attacks the carbonyl carbon of the aldehyde. This step is relatively fast as it involves the formation of a tetrahedral intermediate.

4. **Step 2 - Hydride Transfer**: This is where the hydride ion is transferred from the tetrahedral intermediate of one aldehyde to the carbonyl carbon of another aldehyde. This step is crucial as it determines the formation of the products. It is generally slower than the first step because it involves the breaking of a bond and the formation of a new bond.

5. **Step 3 - Proton Abstraction**: The final step involves the abstraction of a proton from the hydroxyl group of the intermediate. This step is also relatively fast compared to the hydride transfer.

6. **Conclusion**: The slowest step in the Cannizzaro reaction is the second step, which is the transfer of the hydride ion. This step is rate-determining as it directly influences the formation of the final products.

### Final Answer:
The slowest step in the Cannizzaro reaction is the **transfer of hydride to the carbonyl group**.