M-shell can have up to 18 electrons, then why does potassium (Atomic number 19) does not have the electronic configuration 2, 8, 9 ?

Explanation

To understand why potassium (atomic number 19) does not have the electronic configuration of 2, 8, 9, we need to follow these steps:

### Step 1: Understand the Electron Configuration
- The electron configuration of an atom describes how electrons are distributed among the various atomic orbitals. The distribution is based on the atomic number, which indicates the number of electrons in a neutral atom.

### Step 2: Determine the Electron Filling Order
- Electrons fill the shells in a specific order: K shell (1st shell) can hold up to 2 electrons, L shell (2nd shell) can hold up to 8 electrons, and M shell (3rd shell) can hold up to 18 electrons. However, the filling of the M shell is subject to the octet rule.

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