How many electron in Ca (Z =20) have n = 4, l = 0 ?

Options

A. 1
B. 2
C. 3
D. 4

Explanation

To solve the question of how many electrons in calcium (Ca) with atomic number 20 have n = 4 and l = 0, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Quantum Numbers**:
- The principal quantum number (n) indicates the energy level of the electron. Here, n = 4 means we are looking at the 4th energy level.
- The azimuthal quantum number (l) indicates the subshell. For l = 0, this corresponds to the s subshell.

2. **Identify the Relevant Subshell**:
- Since l = 0, we are specifically looking at the 4s subshell.

3. **Write the Electronic Configuration of Calcium**:
- The atomic number of calcium (Ca) is 20. Therefore, the electronic configuration of calcium is:
- 1s² 2s² 2p⁶ 3s² 3p⁶ 4s²
- This configuration shows how the electrons are distributed among the various energy levels and subshells.

4. **Count the Electrons in the 4s Subshell**:
- From the electronic configuration, we can see that the 4s subshell has 2 electrons (4s²).

5. **Conclusion**:
- Therefore, the number of electrons in calcium that have n = 4 and l = 0 is **2**.

### Final Answer:
The number of electrons in Ca (Z = 20) with n = 4 and l = 0 is **2**.

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