Why the maximum covalency of boron is only four where as that of aluminium is six ?

Explanation

To understand why the maximum covalency of boron is only four while that of aluminum is six, we can break down the explanation into several steps:

### Step 1: Understanding Covalency
Covalency refers to the number of bonds an atom can form by sharing its electrons with other atoms. This is largely determined by the number of available orbitals for bonding.

### Step 2: Electron Configuration of Boron
Boron has an atomic number of 5. Its electron configuration is:
- 1s² 2s² 2p¹
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