Which of the following pairs of elements show diagonal relationship ?
1. Li and Mg 2. B and Si 3. Mg and Al Select the correct answer using the codes given below

Options

A. 1 and 3
B. 2 and 3
C. 1 and 2
D. 1,2 and 3

Answer

To determine which pairs of elements show a diagonal relationship, we need to understand what a diagonal relationship is in chemistry. This relationship occurs between certain pairs of elements in the periodic table that are diagonally positioned to each other, typically between the second and third periods.

### Step-by-Step Solution:

1. **Identify the Elements and Their Positions:**
- The pairs given are:
1. Lithium (Li) and Magnesium (Mg)
2. Boron (B) and Silicon (Si)
3. Magnesium (Mg) and Aluminum (Al)

2. **Understand the Concept of Diagonal Relationship:**
- Diagonal relationships occur due to similarities in size and charge between elements that are diagonally adjacent in the periodic table.
- For example, elements in the second period (Li, Be, B, C, N, O, F) can show similarities with elements in the third period (Na, Mg, Al, Si, P, S, Cl).

3. **Analyze Each Pair:**
- **Pair 1: Li and Mg**
- Lithium (Li) is in Group 1 and Period 2, while Magnesium (Mg) is in Group 2 and Period 3. They show similarities in size and properties, indicating a diagonal relationship.
- **Pair 2: B and Si**
- Boron (B) is in Group 13 and Period 2, while Silicon (Si) is in Group 14 and Period 3. They also exhibit similar properties and size, indicating a diagonal relationship.
- **Pair 3: Mg and Al**
- Magnesium (Mg) is in Group 2 and Period 3, while Aluminum (Al) is in Group 13 and Period 3. However, they do not show a diagonal relationship as they are in the same period and do not exhibit similar properties.

4. **Conclusion:**
- The pairs that show a diagonal relationship are:
- 1. Li and Mg
- 2. B and Si
- Therefore, the correct answer is 1 and 2.

### Final Answer:
The correct answer is **1 and 2**.

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