Which of the following order is/are correct?

Options

A. `Mg^(2+)("size") gt Li^(+)` (size)
B. `S(E.A)gtO(E.A)`
C. `Hg(I.E.) gt Cd(I.E)`
D. `P(I.E) gt S(I.E)`

Answer

To determine which of the given orders is correct, we need to analyze each statement based on periodic trends in size, electron affinity, and ionization energy.

### Step 1: Analyze the first order - Size of Mg²⁺ vs Li⁺
- **Statement**: Size of Mg²⁺ is greater than Li⁺.
- **Analysis**: Cations are positively charged ions formed by the loss of electrons. When comparing cations, the charge plays a crucial role in determining size. The greater the positive charge on a cation, the smaller its size due to increased effective nuclear charge acting on the remaining electrons.
- **Conclusion**: Since Mg²⁺ has a +2 charge and Li⁺ has a +1 charge, Mg²⁺ is smaller than Li⁺. Therefore, this statement is **incorrect**.

### Step 2: Analyze the second order - Electron affinity of S vs O
- **Statement**: Electron affinity of sulfur is more than that of oxygen.
- **Analysis**: Electron affinity is the energy change when an electron is added to a neutral atom. Although oxygen is more electronegative, it has a smaller atomic size, which means it cannot accommodate an additional electron as easily as sulfur can. Therefore, sulfur has a higher electron affinity than oxygen.
- **Conclusion**: This statement is **correct**.

### Step 3: Analyze the third order - Ionization energy of Hg vs Cd
- **Statement**: Ionization energy of mercury is more than cadmium.
- **Analysis**: Ionization energy is the energy required to remove an electron from an atom. As we move down a group in the periodic table, ionization energy generally decreases due to the increase in atomic size and the shielding effect. Cadmium (Cd) is above mercury (Hg) in the periodic table, so we expect cadmium to have a higher ionization energy than mercury.
- **Conclusion**: This statement is **incorrect**.

### Step 4: Analyze the fourth order - Ionization energy of P vs S
- **Statement**: Ionization energy of phosphorus is greater than that of sulfur.
- **Analysis**: As we move from left to right across a period, ionization energy increases due to the increasing nuclear charge. Phosphorus (P) is in group 15 and sulfur (S) is in group 16. Since sulfur is to the right of phosphorus, it has a higher ionization energy.
- **Conclusion**: This statement is **incorrect**.

### Final Conclusion
The only correct statement among the options provided is that the electron affinity of sulfur is greater than that of oxygen. Thus, the correct answer is option number 2.

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