The number of electrons in the M-shell of the element with atomic number 18 is :-

Options

A. 12
B. 8
C. 10
D. 6

Explanation

To find the number of electrons in the M-shell of the element with atomic number 18, follow these steps:

### Step 1: Identify the Element
The element with atomic number 18 is Argon (Ar).

**Hint:** The atomic number of an element indicates the number of protons and, in a neutral atom, the number of electrons.

### Step 2: Write the Electronic Configuration
The electronic configuration of Argon can be written as:
1s² 2s² 2p⁶ 3s² 3p⁶

**Hint:** The electronic configuration shows how electrons are distributed among the various atomic orbitals.

### Step 3: Determine the Shells
In the electronic configuration:
- The first shell (K-shell) can hold a maximum of 2 electrons: 1s²
- The second shell (L-shell) can hold a maximum of 8 electrons: 2s² 2p⁶
- The third shell (M-shell) can hold a maximum of 18 electrons, but in Argon, it contains: 3s² 3p⁶

**Hint:** Each shell has a specific capacity for holding electrons (K: 2, L: 8, M: 18).

### Step 4: Count the Electrons in the M-shell
In the M-shell (3rd shell), the electrons are:
- 3s² contributes 2 electrons
- 3p⁶ contributes 6 electrons

Adding these together gives:
2 (from 3s) + 6 (from 3p) = 8 electrons in the M-shell.

**Hint:** To find the total number of electrons in a shell, simply sum the electrons from the subshells within that shell.

### Conclusion
The number of electrons in the M-shell of Argon (atomic number 18) is 8.

**Final Answer:** 8 electrons in the M-shell.

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