Select the correct order of periodic properties of species :

Options

A. `Fe^(2+) lt Fe^(3+)`: Ionic radii
B. `N lt O`: Second ionisation energy
C. `Cu lt Zn`: Atomic radius
D. `In lt Tl` : First ionisation energy

Answer

To solve the question regarding the correct order of periodic properties of species, we will analyze each statement provided and determine their correctness based on periodic trends.

### Step-by-Step Solution:

1. **Comparing the Sizes of Fe²⁺ and Fe³⁺:**
- **Analysis:** Cations are formed when atoms lose electrons. The greater the positive charge of a cation, the smaller its size due to increased nuclear charge pulling the remaining electrons closer to the nucleus.
- **Conclusion:** Fe²⁺ (with a +2 charge) is larger than Fe³⁺ (with a +3 charge). Thus, the statement "Fe²⁺ is smaller than Fe³⁺" is **incorrect**.

2. **Comparing Second Ionization Energies of Oxygen and Nitrogen:**
- **Analysis:** The electronic configuration of nitrogen is 1s² 2s² 2p³, and for oxygen, it is 1s² 2s² 2p⁴. When we remove one electron, nitrogen becomes 1s² 2s² 2p² and oxygen becomes 1s² 2s² 2p³. The second ionization energy involves removing an electron from a more stable configuration (fully filled subshell) in oxygen, which requires more energy.
- **Conclusion:** The second ionization energy of oxygen is greater than that of nitrogen. Thus, the statement is **correct**.

3. **Comparing the Atomic Radius of Copper and Zinc:**
- **Analysis:** As we move across the transition metals from left to right, the atomic radius generally decreases due to increased nuclear charge without a significant increase in shielding. However, copper (Cu) has a filled d-subshell which can lead to a slight increase in size compared to zinc (Zn).
- **Conclusion:** The atomic radius of copper is actually greater than that of zinc, making the statement "the atomic radius of copper is less than zinc" **incorrect**.

4. **Comparing First Ionization Energies of Indium and Thallium:**
- **Analysis:** Indium (In) and thallium (Tl) are both in group 13. As we move down the group, the atomic size increases, and the first ionization energy generally decreases due to increased distance of the outermost electrons from the nucleus and increased shielding effect.
- **Conclusion:** Indium should have a higher first ionization energy than thallium, making the statement "indium has lesser first ionization enthalpy than thallium" **incorrect**.

### Final Conclusion:
The only correct statement is regarding the second ionization energy of oxygen being greater than that of nitrogen. Therefore, the correct order of periodic properties is:

**Correct Answer: Second ionization energy of oxygen > Second ionization energy of nitrogen.**