Which of the following has smallest size ?

Options

A. `Al^(3+)`
B. `Al^(2+)`
C. `Al^(+)`
D. Al

Explanation

To determine which of the following species has the smallest size, we need to analyze the ionic forms of aluminum and their electron configurations. Here’s a step-by-step breakdown of the solution:

### Step 1: Identify the Neutral Atom
We start with the neutral aluminum atom (Al). Aluminum has an atomic number of 13, which means it has 13 protons and, in its neutral state, also 13 electrons.

### Step 2: Understand Ionization
When aluminum loses electrons, it forms cations. The process of ionization involves removing electrons from the outermost shell. The more electrons removed, the more positively charged the ion becomes.

### Step 3: Forming Cations
- **Al (neutral)**: 13 electrons
- **Al⁺ (loses 1 electron)**: 12 electrons
- **Al²⁺ (loses 2 electrons)**: 11 electrons
- **Al³⁺ (loses 3 electrons)**: 10 electrons

### Step 4: Analyze Effective Nuclear Charge
As electrons are removed, the effective nuclear charge (the net positive charge experienced by electrons) increases because there are fewer electrons to shield the nucleus. This means that the nucleus can attract the remaining electrons more strongly.

### Step 5: Compare Sizes
- **Al**: 13 electrons, larger size due to electron-electron repulsion.
- **Al⁺**: Smaller than Al, as it has 12 electrons.
- **Al²⁺**: Smaller than Al⁺, as it has 11 electrons.
- **Al³⁺**: The smallest, with only 10 electrons.

### Conclusion
Among the given species, Al³⁺ has the smallest size because it has the least number of electrons, resulting in a stronger attraction between the nucleus and the remaining electrons.

### Final Answer
The species with the smallest size is **Al³⁺**.

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