Which pair show less similarity in their properties than the other three:

Options

A. Li–Mg
B. Be–Al
C. Na–Ca
D. B–Si

Answer

To determine which pair shows less similarity in their properties than the other three pairs, we can analyze the given pairs based on their positions in the periodic table and the concept of diagonal relationships.

### Step-by-Step Solution:

1. **Identify the Given Pairs**:
- Pair 1: Lithium (Li) and Magnesium (Mg)
- Pair 2: Beryllium (Be) and Aluminium (Al)
- Pair 3: Sodium (Na) and Calcium (Ca)
- Pair 4: Boron (B) and Silicon (Si)

2. **Understand Diagonal Relationships**:
- Diagonal relationships occur between elements in the second and third periods of the periodic table. These elements tend to exhibit similar properties due to their comparable size and charge density.
- For example, Lithium (Li) and Magnesium (Mg) show similarities, as do Beryllium (Be) and Aluminium (Al), and Boron (B) and Silicon (Si).

3. **Analyze Each Pair**:
- **Lithium and Magnesium**: Both are alkali metals and share similar properties such as electronegativity and covalent character.
- **Beryllium and Aluminium**: Both show similar properties, including weak basicity of their hydroxides and similar ionic characteristics.
- **Sodium and Calcium**: These elements belong to different groups (alkali metal and alkaline earth metal) and do not exhibit a diagonal relationship. Their properties are less similar compared to the other pairs.
- **Boron and Silicon**: These elements are also diagonally related and show similarities in their chemical behavior.

4. **Conclusion**:
- The pair that shows less similarity in their properties compared to the other three pairs is **Sodium (Na) and Calcium (Ca)**. This is because they do not exhibit a diagonal relationship and have significantly different properties.

### Final Answer:
**Sodium (Na) and Calcium (Ca) show less similarity in their properties than the other three pairs.**

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