Second element of group `1` shows diagonal relationship with the secound element of group `"_____"` .

Explanation

To solve the question, we need to identify the group in the periodic table that has a diagonal relationship with the second element of group 1, which is lithium.

### Step-by-Step Solution:

1. **Identify the Second Element of Group 1**:
- Group 1 of the periodic table consists of alkali metals. The first element is Hydrogen (H), and the second element is Lithium (Li).

2. **Understand Diagonal Relationships**:
- Diagonal relationships in the periodic table occur between certain pairs of elements in adjacent groups. These relationships arise due to similarities in size and charge, which can lead to similar chemical properties.

3. **Identify the Second Element of Group 2**:
- Group 2 of the periodic table consists of alkaline earth metals. The first element is Beryllium (Be), and the second element is Magnesium (Mg).

4. **Establish the Diagonal Relationship**:
- Lithium (Li) from Group 1 shows a diagonal relationship with Magnesium (Mg) from Group 2. This is due to their similar electronegativity and other chemical properties.

5. **Fill in the Blank**:
- The question asks for the group number that corresponds to the second element (Mg) that shows a diagonal relationship with Li. Since Mg is the second element of Group 2, the answer to fill in the blank is "2".

### Final Answer:
The second element of group 1 (Lithium) shows a diagonal relationship with the second element of group **2** (Magnesium).

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