If an element A belongs to period 3 and group 2, then it will have

Options

A. 3 shells and 2 valence electrons
B. 2 shells and 3 valence electrons
C. 3 shells and 3 valence electrons
D. 2 shells and 2 valence electrons

Explanation

To solve the question, we need to identify the properties of an element A that belongs to period 3 and group 2 of the periodic table. Here’s a step-by-step breakdown:

### Step 1: Identify the Element
- Elements in **Group 2** (the alkaline earth metals) include Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), and Barium (Ba).
- Elements in **Period 3** include Sodium (Na), Magnesium (Mg), Aluminum (Al), Silicon (Si), Phosphorus (P), Sulfur (S), Chlorine (Cl), and Argon (Ar).
- The only element that is both in **Group 2** and **Period 3** is **Magnesium (Mg)**.

**Hint:** Look for the intersection of the specified period and group in the periodic table.

### Step 2: Determine the Atomic Number
- The atomic number of Magnesium (Mg) is **12**.

**Hint:** Recall that the atomic number indicates the number of protons and also the total number of electrons in a neutral atom.

### Step 3: Write the Electronic Configuration
- The electronic configuration of Magnesium is:
- 1s² 2s² 2p⁶ 3s²
- This shows that Magnesium has:
- **3 shells** (1st shell: 1s, 2nd shell: 2s and 2p, 3rd shell: 3s)
- **2 electrons in the outermost shell** (3s²).

**Hint:** The electronic configuration helps determine the number of shells and valence electrons.

### Step 4: Analyze the Options
Now, let's analyze the provided options:
1. **3 shells and 2 valence electrons** - This matches our findings.
2. **2 shells and 3 valence electrons** - Incorrect, as Magnesium has 3 shells.
3. **3 shells and 3 valence electrons** - Incorrect, as Magnesium has only 2 valence electrons.
4. **2 shells and 2 valence electrons** - Incorrect, as Magnesium has 3 shells.

**Hint:** Compare each option with the determined properties of Magnesium.

### Conclusion
The correct answer is **3 shells and 2 valence electrons**.

**Final Answer:** The element A has **3 shells and 2 valence electrons**.