In which pair the first atom or ion is not larger than the second :-

Options

A. N,F
B. `Cl^(-),Cl`
C. `O,S`
D. `Fe^(2+),Fe^(3+)`

Answer

To solve the question "In which pair the first atom or ion is not larger than the second?", we will analyze each of the given pairs of atoms or ions to determine their relative sizes.

### Step 1: Analyze the first pair - Nitrogen (N) and Phosphorus (P)
- **Atomic Size Trend**: Atomic size increases down a group in the periodic table.
- **Comparison**: Nitrogen is in the 2nd period, while Phosphorus is in the 3rd period. Therefore, Nitrogen is smaller than Phosphorus.
- **Conclusion**: N < P

### Step 2: Analyze the second pair - Chloride ion (Cl⁻) and Chlorine atom (Cl)
- **Charge Effect on Size**: Anions are larger than their neutral atoms due to the addition of an electron which increases electron-electron repulsion.
- **Comparison**: Cl⁻ has gained an electron compared to Cl, making Cl⁻ larger than Cl.
- **Conclusion**: Cl < Cl⁻

### Step 3: Analyze the third pair - Oxygen (O) and Sulfur (S)
- **Atomic Size Trend**: Similar to the first pair, atomic size increases down a group.
- **Comparison**: Oxygen is in the 2nd period, while Sulfur is in the 3rd period. Therefore, Oxygen is smaller than Sulfur.
- **Conclusion**: O < S

### Step 4: Analyze the fourth pair - Iron (Fe²⁺) and Iron (Fe³⁺)
- **Charge Effect on Size**: Cations decrease in size with an increase in positive charge due to increased nuclear attraction on the remaining electrons.
- **Comparison**: Fe²⁺ has lost 2 electrons, while Fe³⁺ has lost 3 electrons. Thus, Fe²⁺ is larger than Fe³⁺.
- **Conclusion**: Fe²⁺ > Fe³⁺

### Final Conclusion
From the analysis:
- Pair A: N < P (N is not larger than P)
- Pair B: Cl < Cl⁻ (Cl is not larger than Cl⁻)
- Pair C: O < S (O is not larger than S)
- Pair D: Fe²⁺ > Fe³⁺ (Fe²⁺ is larger than Fe³⁺)

The correct answer to the question is **Option C: O and S**, as in this pair, the first atom (O) is not larger than the second atom (S).