The value of `II^(nd)Delta_(eg)H` of O & S respectively in KJ/mole :-

Options

A. `+580, +780`
B. `+780, +580`
C. `+580, –780`
D. ` –780, –580`

Explanation

To determine the second electron gain enthalpy (ΔE_GH) for oxygen (O) and sulfur (S), we need to follow these steps:

### Step 1: Understand Electron Gain Enthalpy
Electron gain enthalpy is defined as the energy change when an electron is added to an isolated gaseous atom. The first electron gain enthalpy (ΔE_GH1) is usually negative because energy is released when an electron is added. However, the second electron gain enthalpy (ΔE_GH2) is typically positive because adding a second electron to a negatively charged ion involves overcoming repulsion between the electrons.

**Hint:** Remember that the first electron gain enthalpy is usually negative, while the second is positive due to electron-electron repulsion.

### Step 2: Write the Reactions
For oxygen:
1. O(g) + e⁻ → O⁻(g) (First electron gain enthalpy, ΔE_GH1)
2. O⁻(g) + e⁻ → O²⁻(g) (Second electron gain enthalpy, ΔE_GH2)

For sulfur:
1. S(g) + e⁻ → S⁻(g) (First electron gain enthalpy, ΔE_GH1)
2. S⁻(g) + e⁻ → S²⁻(g) (Second electron gain enthalpy, ΔE_GH2)

**Hint:** Write down the reactions for both elements to visualize the process of adding electrons.

### Step 3: Analyze the Second Electron Gain Enthalpy
Both O and S will have a positive ΔE_GH2 because we are adding an electron to a negatively charged ion (O⁻ or S⁻). The repulsion between the electrons will require energy input.

**Hint:** Consider the size of the ions; smaller ions will have greater electron-electron repulsion when adding another electron.

### Step 4: Compare Oxygen and Sulfur
Oxygen (O⁻) is smaller in size compared to sulfur (S⁻). Therefore, the electron-electron repulsion in O⁻ will be greater than in S⁻. This means that the second electron gain enthalpy for oxygen will be higher than that for sulfur.

**Hint:** Think about how the size of the ions affects the repulsion between electrons.

### Step 5: State the Values
From the information provided:
- The second electron gain enthalpy for oxygen (ΔE_GH2 for O) is approximately +780 kJ/mol.
- The second electron gain enthalpy for sulfur (ΔE_GH2 for S) is approximately +580 kJ/mol.

**Hint:** Use the values given to summarize your findings.

### Final Answer
The values of the second electron gain enthalpy (ΔE_GH) for oxygen and sulfur are:
- ΔE_GH2 (O) = +780 kJ/mol
- ΔE_GH2 (S) = +580 kJ/mol