In which series are the species listed in order of increasing size ?

Options

A. `N,O,F`
B. `Na,Mg,K`
C. `Cr,Cr^(2+),Cr^(3+)`
D. `CI,CI^(-),S^(2-)`

Answer

To determine the order of increasing size among the given species, we need to analyze the trends in atomic and ionic sizes based on their positions in the periodic table.

### Step-by-Step Solution:

1. **Understand the Trends in Size**:
- Atomic size increases down a group and decreases across a period.
- Cations (positively charged ions) are smaller than their parent atoms because they lose electrons, leading to less electron-electron repulsion.
- Anions (negatively charged ions) are larger than their parent atoms because they gain electrons, leading to increased electron-electron repulsion.

2. **Identify the Given Species**:
- The species given are: Cr²⁺, Cr³⁺, Cl, Cl⁻, and S²⁻.

3. **Analyze the Cations**:
- For the cations Cr²⁺ and Cr³⁺, as the positive charge increases from Cr²⁺ to Cr³⁺, the size decreases. Therefore, Cr³⁺ < Cr²⁺.

4. **Analyze the Neutral Atom and Anions**:
- Cl is a neutral atom, while Cl⁻ and S²⁻ are anions.
- As we move from Cl to Cl⁻, the size increases because Cl⁻ has gained an electron.
- S²⁻ is larger than Cl⁻ because it has gained two electrons, leading to greater electron-electron repulsion.

5. **Establish the Order**:
- Now we can order the species based on size:
- Cr³⁺ < Cr²⁺ < Cl < Cl⁻ < S²⁻

### Final Order of Increasing Size:
- Cr³⁺ < Cr²⁺ < Cl < Cl⁻ < S²⁻