According to hard and soft acid base principle, a hard acid

Options

A. Has low charge density
B. Shows preference for soft bases
C. Shows preference for donor atoms of low electronegativity
D. Is not polarizable

Explanation

### Step-by-Step Solution:

1. **Understanding Hard and Soft Acids and Bases**:
- The Hard and Soft Acid-Base (HSAB) principle categorizes acids and bases based on their properties. Hard acids and bases are characterized by high charge density and low polarizability.

2. **Defining Hard Acids**:
- Hard acids are typically small, highly charged cations. They have a high charge density, meaning they possess a significant amount of charge relative to their size. Examples include H⁺, Li⁺, Na⁺, and Al³⁺.

3. **Defining Hard Bases**:
- Hard bases are usually small anions or neutral molecules with high electronegativity and low polarizability. Examples include OH⁻, F⁻, and NH₃.

4. **Preference of Hard Acids and Bases**:
- According to the HSAB principle, hard acids prefer to react with hard bases. This is because both hard acids and bases have high charge densities and low polarizability, leading to stronger ionic interactions.

5. **Charge Density and Polarizability**:
- Hard acids and bases have high charge density, which means they can interact strongly with each other. They are also non-polarizable, meaning their electron clouds do not easily distort, which is crucial for maintaining strong ionic bonds.

6. **Conclusion**:
- Therefore, hard acids are preferred to bind with hard bases due to their compatibility in terms of charge density and polarizability.

### Final Answer:
According to the Hard and Soft Acid-Base principle, a hard acid is characterized by high charge density and low polarizability, and it prefers to bind with hard bases.