Three elements 'X', 'Y' and 'Z' have atomic numbers 18, 19 and 20 respectively. How many electrons are present in the M shell of these elements?

Options

A. `8, 9, 10`
B. `8, 10, 13`
C. `8, 8, 8`
D. `8, 9, 12`

Explanation

To determine how many electrons are present in the M shell of the elements X, Y, and Z with atomic numbers 18, 19, and 20 respectively, we can follow these steps:

### Step 1: Identify the atomic numbers and corresponding electrons
- Element X has an atomic number of 18, which means it has 18 electrons.
- Element Y has an atomic number of 19, which means it has 19 electrons.
- Element Z has an atomic number of 20, which means it has 20 electrons.

### Step 2: Determine the electron configuration
The electron configuration is distributed among the shells as follows:
- The K shell can hold a maximum of 2 electrons.
- The L shell can hold a maximum of 8 electrons.
- The M shell can hold a maximum of 18 electrons, but we will only fill it according to the number of electrons available.

#### For Element X (18 electrons):
- K shell: 2 electrons
- L shell: 8 electrons
- M shell: 8 electrons (18 - 2 - 8 = 8)

#### For Element Y (19 electrons):
- K shell: 2 electrons
- L shell: 8 electrons
- M shell: 9 electrons (19 - 2 - 8 = 9)

#### For Element Z (20 electrons):
- K shell: 2 electrons
- L shell: 8 electrons
- M shell: 10 electrons (20 - 2 - 8 = 10)

### Step 3: Count the electrons in the M shell
- Element X has 8 electrons in the M shell.
- Element Y has 9 electrons in the M shell.
- Element Z has 10 electrons in the M shell.

### Conclusion
The number of electrons present in the M shell of elements X, Y, and Z are:
- X: 8 electrons
- Y: 9 electrons
- Z: 10 electrons

### Final Answer
The M shell contains 8, 9, and 10 electrons for elements X, Y, and Z respectively.

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