For an atomic number 20, the 20th electron will occupy

Options

A. L-shell
B. M-shell
C. N-shell
D. K-shell

Explanation

To determine where the 20th electron will occupy for an atomic number of 20, we will follow these steps:

### Step 1: Identify the atomic number
The atomic number (Z) is given as 20. This means the element has 20 electrons.

### Step 2: Understand electron configuration
Electrons are filled in atomic orbitals following the Aufbau principle, which states that electrons occupy the lowest energy orbitals first. The order of filling is generally K, L, M, N shells.

### Step 3: Determine the maximum number of electrons in each shell
- K shell can hold a maximum of 2 electrons.
- L shell can hold a maximum of 8 electrons.
- M shell can hold a maximum of 18 electrons (but we will only fill up to the 20th electron).

### Step 4: Fill the K shell
The K shell will be filled first:
- K shell: 2 electrons (total = 2)

### Step 5: Fill the L shell
Next, we fill the L shell:
- L shell: 8 electrons (total = 2 + 8 = 10)

### Step 6: Fill the M shell
Now, we fill the M shell:
- M shell: 8 electrons (total = 10 + 8 = 18)

### Step 7: Determine the position of the 20th electron
At this point, we have filled 18 electrons. The next electron, which is the 19th, will go into the M shell, and the 20th electron will also occupy the M shell.

### Conclusion
Thus, the 20th electron will occupy the M shell.

### Final Answer
The 20th electron will occupy the M shell.

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