Which of these ions is smallest in size?

Options

A. `O^(2– )`
B. `C^(4– )`
C. `F^– `
D. `N^(3–) `

Answer

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

### Step 1: Identify the ions
First, we need to identify the ions in question. Let's assume we have the following ions: O²⁻ (oxide), F⁻ (fluoride), N³⁻ (nitride), and C⁴⁻ (carbide).

### Step 2: Understand the concept of ionic size
Ionic size is influenced by the number of electrons and protons in an ion. Anions (negatively charged ions) are formed when atoms gain electrons. The size of an anion increases with the addition of electrons due to increased electron-electron repulsion.

### Step 3: Compare the ions
- **O²⁻ (oxide ion)**: Gains 2 electrons.
- **F⁻ (fluoride ion)**: Gains 1 electron.
- **N³⁻ (nitride ion)**: Gains 3 electrons.
- **C⁴⁻ (carbide ion)**: Gains 4 electrons.

As we add more electrons, the size of the ion increases due to increased repulsion among the electrons.

### Step 4: Analyze the trend in ionic size
When comparing anions from the same period, the size decreases as we move from left to right across the periodic table because of the increasing effective nuclear charge. However, when comparing anions with different numbers of electrons, the more electrons an ion has, the larger it is.

### Step 5: Determine the smallest ion
Among the ions listed:
- O²⁻ has gained 2 electrons.
- F⁻ has gained 1 electron.
- N³⁻ has gained 3 electrons.
- C⁴⁻ has gained 4 electrons.

Since F⁻ has gained the least number of electrons, it will have the smallest ionic size compared to the others.

### Conclusion
Thus, the smallest ion among the given options is **F⁻ (fluoride ion)**.

### Final Answer
The smallest ion is **F⁻ (fluoride)**.

---