Which of the following is the largest in size ?

Options

A. `S ^(2-)`
B. `Se ^(2-)`
C. `O ^(2-)`
D. `Te ^(2-)`

Explanation

To determine which of the given anions is the largest in size, we can follow these steps:

### Step 1: Identify the elements and their anions
The question provides us with the following anions:
- S²⁻ (sulfide anion)
- Se²⁻ (selenide anion)
- O²⁻ (oxide anion)
- Te²⁻ (telluride anion)

### Step 2: Determine the group of the elements
All these elements belong to Group 16 of the periodic table, which is also known as the chalcogens. The order of the elements in this group from top to bottom is:
- Oxygen (O)
- Sulfur (S)
- Selenium (Se)
- Tellurium (Te)

### Step 3: Understand the trend in atomic size
In general, as we move down a group in the periodic table, the size of the atoms (and their corresponding anions) increases. This is due to the addition of new electron shells, which increases the distance between the nucleus and the outermost electrons.

### Step 4: Consider the effect of gaining electrons
When an atom gains electrons to form an anion, it becomes larger due to increased electron-electron repulsion. However, the trend of size increase due to additional electron shells still holds.

### Step 5: Compare the sizes of the anions
- O²⁻: Oxygen is at the top of Group 16 and has the smallest size.
- S²⁻: Sulfur is below oxygen and larger than O²⁻.
- Se²⁻: Selenium is below sulfur and larger than S²⁻.
- Te²⁻: Tellurium is at the bottom of the group and has the largest size.

### Conclusion
Based on the periodic trend and the addition of electron shells, the largest anion among the given options is Te²⁻ (telluride anion).

### Final Answer
The largest in size is Te²⁻ (telluride anion).

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