Which one of the following statements is correct ?

Options

A. All boron trihalides are completely hydrolysed to boric acid.
B. `BF_3` undergo partial hydrolysis to form fluroboric acid and boric acid.
C. Aluminium halides make up the electron deficiency by bridging with halides .
D. None of these

Explanation

To solve the question regarding which statement is correct among the given options, we will analyze each statement step by step.

### Step 1: Analyze the first statement
The first statement claims that "all boron trihalides are completely hydrolyzed to boric acid."

- **Explanation**: Boron trihalides (BX3) typically undergo hydrolysis. However, BF3 (boron trifluoride) does not undergo complete hydrolysis due to the strength of the B-F bond. Instead, it undergoes partial hydrolysis, producing both boric acid (H3BO3) and fluoroboric acid (HBF4).

- **Conclusion**: This statement is **false**.

### Step 2: Analyze the second statement
The second statement claims that "BF3 undergoes partial hydrolysis to form chloroforic and boric acid."

- **Explanation**: As mentioned earlier, BF3 does undergo partial hydrolysis, leading to the formation of boric acid and fluoroboric acid (HBF4). The term "chloroforic" seems to be a typographical error, as it should refer to "fluoroboric."

- **Conclusion**: This statement is **true**.

### Step 3: Analyze the third statement
The third statement claims that "aluminium halides make up the electron deficiency by bridging with halides."

- **Explanation**: Aluminium halides (like AlCl3) are known to form dimers (e.g., Al2Cl6) in which the electron deficiency is compensated by bridging between aluminum and halide atoms. This bridging helps to stabilize the dimeric form.

- **Conclusion**: This statement is **true**.

### Final Conclusion
Based on the analysis:
- The first statement is false.
- The second statement is true.
- The third statement is true.

Thus, the correct statements are **option 2 and option 3**.