An element lies In third period and second group of the periodic table. Select the false statement about the atom of this element.

Options

A. It has three valence electrons
B. It has three shells
C. It has two valence electrons
D. It has 12 electrons

Explanation

To solve the question, we need to identify the element that lies in the third period and the second group of the periodic table, and then determine which statement about this element is false.

### Step-by-Step Solution:

1. **Identify the Element**:
- The third period of the periodic table includes the elements from sodium (Na) to argon (Ar).
- The second group of the periodic table consists of alkaline earth metals, which includes beryllium (Be), magnesium (Mg), calcium (Ca), etc.
- The element that lies in the third period and second group is **Magnesium (Mg)**.

2. **Determine the Atomic Number**:
- Magnesium has an atomic number of 12.

3. **Electron Configuration**:
- The electron configuration of magnesium can be determined as follows:
- K shell can hold 2 electrons.
- L shell can hold 8 electrons.
- M shell can hold 2 electrons.
- Therefore, the electron configuration of magnesium is:
- 2 electrons in K shell, 8 electrons in L shell, and 2 electrons in M shell.
- This can be represented as: 1s² 2s² 2p⁶ 3s².

4. **Valence Electrons**:
- Valence electrons are the electrons in the outermost shell. For magnesium, the outermost shell (M shell) has 2 electrons.
- Thus, magnesium has **2 valence electrons**.

5. **Evaluate the Statements**:
- Now we need to evaluate the statements provided about magnesium:
- Statement 1: It has three valence electrons. (False, it has 2 valence electrons)
- Statement 2: It has three shells. (True, K, L, and M shells)
- Statement 3: It has two valence electrons. (True)
- Statement 4: It has 12 electrons. (True, as its atomic number is 12)

6. **Conclusion**:
- The false statement about magnesium is that it has three valence electrons. Therefore, the answer to the question is that the false statement is the one claiming it has three valence electrons.

### Final Answer:
The false statement about the atom of magnesium is: **It has three valence electrons.**