The first ionisation energy of first atom is greater than that of second atom, whereas reverse order is true for their second ionisation energy. Which set of elements is in accordance to above statement?

Options

A. CgtB
B. PgtS
C. BegtB
D. MggtNa

Answer

To solve the question, we need to analyze the ionization energies of the given elements and determine which set of elements fits the criteria described in the question.

### Step-by-Step Solution:

1. **Understanding Ionization Energy**:
- The first ionization energy (IE1) is the energy required to remove the outermost electron from a neutral atom.
- The second ionization energy (IE2) is the energy required to remove the second electron after the first has been removed.

2. **Analyzing the Given Sets**:
- We need to find a pair of elements where the first ionization energy of the first element is greater than that of the second, and the second ionization energy of the second element is greater than that of the first.

3. **Evaluating Each Option**:
- **Option 1: Carbon (C) and Boron (B)**
- C (Z=6): 1s² 2s² 2p²
- B (Z=5): 1s² 2s² 2p¹
- IE1(C) > IE1(B) (C has a higher first ionization energy)
- IE2(B) > IE2(C) (B becomes stable after losing one electron)
- **This option fits the criteria.**

- **Option 2: Phosphorus (P) and Sulfur (S)**
- P (Z=15): 1s² 2s² 2p⁶ 3s² 3p³
- S (Z=16): 1s² 2s² 2p⁶ 3s² 3p⁴
- IE1(P) > IE1(S) (P has a higher first ionization energy)
- IE2(S) > IE2(P) (S becomes stable after losing one electron)
- **This option fits the criteria.**

- **Option 3: Beryllium (Be) and Boron (B)**
- Be (Z=4): 1s² 2s²
- B (Z=5): 1s² 2s² 2p¹
- IE1(Be) > IE1(B) (Be has a higher first ionization energy)
- IE2(B) > IE2(Be) (B becomes stable after losing one electron)
- **This option fits the criteria.**

- **Option 4: Magnesium (Mg) and Sodium (Na)**
- Mg (Z=12): 1s² 2s² 2p⁶ 3s²
- Na (Z=11): 1s² 2s² 2p⁶ 3s¹
- IE1(Mg) > IE1(Na) (Mg has a higher first ionization energy)
- IE2(Na) > IE2(Mg) (Na becomes stable after losing one electron)
- **This option fits the criteria.**

4. **Conclusion**:
- All four options (1, 2, 3, and 4) fit the criteria of the question, as they all show that the first ionization energy of the first atom is greater than that of the second atom, while the reverse is true for their second ionization energy.

### Final Answer:
All options (1, 2, 3, and 4) are correct.