The main group elements i.e. representative elements complete their electron configuration using s and p electrons in the periodic table. These elements range from the most metallic to the most non-metallic with intermediate properties, the semi-metals, in between .The elements which occur at the two extremes of the periodic table are highly reactive and therefore, these highly reactive elements do not occur in free state : they usually occur in the combined forms.
Beryllium and aluminium exhibit many properties which are similar, but, the two elements differ in :

Options

A. Forming covalent halides
B. Forming polymeric hydrides
C. Exhibiting maximum covalency in compounds
D. Exhibiting amphoteric nature in their oxides

Explanation

To solve the question regarding the differences between beryllium and aluminum, we need to analyze their properties and how they relate to their positions in the periodic table. Here’s a step-by-step breakdown:

### Step 1: Identify the Elements
- **Beryllium (Be)**: Atomic number 4, located in Group 2 (alkaline earth metals).
- **Aluminum (Al)**: Atomic number 13, located in Group 13 (p-block element).

### Step 2: Understand the Diagonal Relationship
- Beryllium and aluminum are diagonally adjacent in the periodic table. This diagonal relationship often leads to similarities in properties due to comparable electronegativity and ionic sizes.

### Step 3: Compare Covalent Bonding
- Both beryllium and aluminum tend to form covalent bonds. For example, both form covalent chlorides (BeCl2 and AlCl3), which are soluble in organic solvents.

### Step 4: Examine Covalency
- **Beryllium** can exhibit a maximum covalency of 4 due to its electronic configuration and lack of vacant d-orbitals.
- **Aluminum**, on the other hand, can exhibit a maximum covalency of 6 because it has vacant d-orbitals that allow for additional bonding.

### Step 5: Analyze Amphoteric Nature
- Both beryllium oxide (BeO) and aluminum oxide (Al2O3) are amphoteric, meaning they can react with both acids and bases. This property is similar for both elements.

### Conclusion
- The primary difference between beryllium and aluminum lies in their maximum covalency in compounds. Beryllium has a maximum covalency of 4, while aluminum can reach a covalency of 6 due to the presence of vacant d-orbitals.

### Final Answer
- Beryllium and aluminum differ in exhibiting maximum covalency in compounds.

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