Which of the following statements is not true for both B and Al ?

Options

A. They burn in oxygen to give oxides at high temperature
B. Their halides are Lewis acids
C. They combine with nitrogen to form nitrides
D. They react with HCl to from chlorides

Answer

To solve the question "Which of the following statements is not true for both B (Boron) and Al (Aluminum)?", we will analyze each statement provided in the options.

### Step-by-Step Solution:

1. **Understanding the Elements**:
- Boron (B) and Aluminum (Al) are both in Group 13 of the periodic table. They share some similar properties due to their group placement.

2. **Analyzing Each Statement**:
- **Statement 1**: "They burn in oxygen to give the oxide at high temperature."
- **Boron** reacts with oxygen to form Boron trioxide (B2O3).
- **Aluminum** reacts with oxygen to form Aluminum oxide (Al2O3).
- **Conclusion**: This statement is true for both elements.

- **Statement 2**: "Their halides are Lewis acids."
- **Boron halides** (e.g., BCl3) are known to act as Lewis acids because they have an incomplete octet.
- **Aluminum halides** (e.g., AlCl3) also act as Lewis acids for the same reason.
- **Conclusion**: This statement is true for both elements.

- **Statement 3**: "They combine with nitrogen to form nitride."
- **Boron** reacts with nitrogen to form Boron nitride (BN).
- **Aluminum** reacts with nitrogen to form Aluminum nitride (AlN).
- **Conclusion**: This statement is true for both elements.

- **Statement 4**: "They react with HCl to form Chloride."
- **Aluminum** reacts with hydrochloric acid (HCl) to form Aluminum chloride (AlCl3) and hydrogen gas (H2).
- **Boron**, however, does not react with HCl to form Boron chloride (BCl3) under normal conditions due to its small size and high ionization energy, which makes it difficult to lose electrons.
- **Conclusion**: This statement is **not true** for Boron.

3. **Final Conclusion**: The statement that is not true for both B and Al is **Statement 4**: "They react with HCl to form Chloride."