Which of the following has the largest ionic radius ?

Options

A. `Be^(2+)`
B. `Mg^(2+)`
C. `Ca^(2+)`
D. `Sr^(2+)`

Explanation

To determine which of the given ions has the largest ionic radius, we will analyze the options provided: Beryllium 2+ (Be²⁺), Magnesium 2+ (Mg²⁺), Calcium 2+ (Ca²⁺), and Strontium 2+ (Sr²⁺).

### Step-by-Step Solution:

1. **Identify the Group**: All the given elements belong to Group 2 of the periodic table, which is also known as the alkaline earth metals.

2. **Understand Ionic Radius Trend**: The ionic radius generally increases as you move down a group in the periodic table. This is because as you go down a group, additional electron shells are added, which increases the distance between the nucleus and the outermost electrons.

3. **List the Elements**: The elements in Group 2 are:
- Beryllium (Be)
- Magnesium (Mg)
- Calcium (Ca)
- Strontium (Sr)

4. **Consider the Ionic Forms**: We are looking at the 2+ ions of these elements:
- Be²⁺
- Mg²⁺
- Ca²⁺
- Sr²⁺

5. **Analyze the Ionic Sizes**:
- Beryllium (Be) has the smallest atomic size and thus the smallest ionic radius when it forms Be²⁺.
- Magnesium (Mg) is larger than Beryllium, so Mg²⁺ will have a larger radius than Be²⁺.
- Calcium (Ca) is larger than Magnesium, so Ca²⁺ will have a larger radius than Mg²⁺.
- Strontium (Sr) is the largest of the four elements, so Sr²⁺ will have the largest ionic radius.

6. **Conclusion**: Based on the trend that ionic radius increases down the group, we can conclude that the ionic radius of Sr²⁺ is larger than that of Ca²⁺, Mg²⁺, and Be²⁺.

### Final Answer:
The ion with the largest ionic radius is **Strontium 2+ (Sr²⁺)**.