An element with atomic number 20 will be placed in which period of the periodic table

Options

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

Answer

To determine in which period of the periodic table an element with atomic number 20 is placed, we can follow these steps:

### Step 1: Identify the Element
The element with atomic number 20 is Calcium (Ca).

### Step 2: Write the Electronic Configuration
To find the electronic configuration of Calcium, we start filling the orbitals according to the Aufbau principle. The electronic configuration for Calcium is:
- 1s² 2s² 2p⁶ 3s² 3p⁶ 4s²
This can also be represented as:
- [Ne] 4s² (where [Ne] represents the electron configuration of Neon, which is 1s² 2s² 2p⁶).

### Step 3: Determine the Valence Shell
The valence shell is the outermost shell that contains electrons. For Calcium, the outermost shell is the 4th shell (4s²).

### Step 4: Identify the Principal Quantum Number
The principal quantum number (n) corresponds to the energy level of the valence shell. In this case, since the valence electrons are in the 4s orbital, the principal quantum number (n) is 4.

### Step 5: Determine the Period
The period of an element in the periodic table corresponds to the principal quantum number of its valence shell. Since n = 4 for Calcium, it is located in the 4th period of the periodic table.

### Conclusion
Thus, the element with atomic number 20 (Calcium) is placed in the **4th period** of the periodic table.

### Answer
The correct option is: **4th Period**

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