How many electron in Ca (Z =20) have n = 3, l = 0 ?

Options

A. 2
B. 0
C. 1
D. 3

Explanation

To solve the question of how many electrons in calcium (Ca) with atomic number Z = 20 have the principal quantum number n = 3 and azimuthal quantum number l = 0, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Atomic Number**:
The atomic number of calcium (Ca) is 20. This means calcium has 20 electrons.

2. **Write the Electronic Configuration**:
The electronic configuration of calcium can be written as:
\[ \text{Ca: } 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^2 \]
This configuration accounts for all 20 electrons.

3. **Identify the Quantum Numbers**:
- The principal quantum number (n) is given as 3.
- The azimuthal quantum number (l) is given as 0.
- When l = 0, it corresponds to the s orbital.

4. **Determine the Relevant Orbital**:
Since n = 3 and l = 0, we are looking at the 3s orbital.

5. **Count the Electrons in the 3s Orbital**:
From the electronic configuration, the 3s orbital has:
\[ 3s^2 \]
This indicates that there are 2 electrons in the 3s orbital.

### Final Answer:
Therefore, the number of electrons in calcium (Ca) with n = 3 and l = 0 is **2**.

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