Which of the following has smallest radius?

Options

A. `1s^(2), 2s^(2)2p^(6), 3s^(2)`
B. `1s^(2), 2s^(2)2p^(6), 3s^(2)3p^(1)`
C. `1s^(2), 2s^(2)2p^(6),3s^(2)3p^(5)`
D. `1s^(2),2s^(2)2p^(6),3s^(2)3p^(3)`

Answer

To determine which of the given elements has the smallest atomic radius, we can follow these steps:

### Step 1: Identify the Elements
The elements mentioned in the question are:
- Magnesium (Mg): 1s² 2s² 2p⁶ 3s²
- Aluminum (Al): 1s² 2s² 2p⁶ 3s² 3p¹
- Phosphorus (P): 1s² 2s² 2p⁶ 3s² 3p³
- Chlorine (Cl): 1s² 2s² 2p⁶ 3s² 3p⁵

### Step 2: Understand the Periodic Trend
Atomic radius decreases as you move from left to right across a period in the periodic table. This is due to the increase in the effective nuclear charge (Z-effective) experienced by the outermost electrons. As protons are added to the nucleus, the positive charge increases, pulling the electrons closer to the nucleus and resulting in a smaller atomic radius.

### Step 3: Analyze the Elements in the Third Period
In the third period, we have:
- Magnesium (Mg) - Group 2
- Aluminum (Al) - Group 13
- Phosphorus (P) - Group 15
- Chlorine (Cl) - Group 17

As we move from magnesium to chlorine, we are moving from left to right across the period.

### Step 4: Compare the Atomic Radius
- Magnesium (Mg) has the largest atomic radius because it is on the far left.
- Aluminum (Al) has a smaller radius than magnesium.
- Phosphorus (P) has a smaller radius than aluminum.
- Chlorine (Cl) has the smallest radius among these elements because it is on the far right.

### Conclusion
Chlorine (Cl) has the smallest atomic radius among the given elements.

### Final Answer
**Chlorine (Cl)** has the smallest radius.

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