Which of the following pair contains 2 lone pairs of electrons on the central atom?

Options

A. `I_(2), H_(2)O`
B. `H_(2)O, NF_(3)`
C. `XeF_(4), NH_(3)`
D. `SO_(4)^(2-), H_(2)S`

Answer

To determine which of the following pairs contains 2 lone pairs of electrons on the central atom, we need to analyze the molecular structures of the given compounds. Here’s how to approach the problem step by step:

### Step 1: Identify the central atom and its valence electrons
For each compound, identify the central atom and count its valence electrons.

### Step 2: Draw the Lewis structure
Using the valence electrons, draw the Lewis structure for each compound. This will help visualize the number of bonds and lone pairs.

### Step 3: Count the lone pairs
After drawing the Lewis structure, count the number of lone pairs on the central atom.

### Step 4: Compare the compounds
Compare the lone pairs counted for each compound to see which ones have 2 lone pairs.

### Step 5: Identify the correct answer
Select the compound(s) that have 2 lone pairs on the central atom.

### Detailed Solution:

1. **I3⁻ (Iodine triiodide ion)**:
- Central atom: Iodine (I)
- Valence electrons: Iodine has 7 valence electrons. In I3⁻, it loses one electron, so it has 6 valence electrons.
- Lewis structure: Iodine forms bonds with two other iodine atoms using 2 electrons and retains 2 lone pairs.
- Lone pairs: 2 lone pairs on the central iodine atom.

2. **H2O (Water)**:
- Central atom: Oxygen (O)
- Valence electrons: Oxygen has 6 valence electrons.
- Lewis structure: Oxygen forms 2 bonds with hydrogen atoms using 2 electrons and retains 2 lone pairs.
- Lone pairs: 2 lone pairs on the central oxygen atom.

3. **NF3 (Nitrogen trifluoride)**:
- Central atom: Nitrogen (N)
- Valence electrons: Nitrogen has 5 valence electrons.
- Lewis structure: Nitrogen forms 3 bonds with fluorine atoms using 3 electrons and retains 1 lone pair.
- Lone pairs: 1 lone pair on the central nitrogen atom.

4. **XeF4 (Xenon tetrafluoride)**:
- Central atom: Xenon (Xe)
- Valence electrons: Xenon has 8 valence electrons.
- Lewis structure: Xenon forms 4 bonds with fluorine atoms using 4 electrons and retains 2 lone pairs.
- Lone pairs: 2 lone pairs on the central xenon atom.

5. **H2S (Hydrogen sulfide)**:
- Central atom: Sulfur (S)
- Valence electrons: Sulfur has 6 valence electrons.
- Lewis structure: Sulfur forms 2 bonds with hydrogen atoms using 2 electrons and retains 2 lone pairs.
- Lone pairs: 2 lone pairs on the central sulfur atom.

6. **SFO2⁻ (Thiofluorosulfate ion)**:
- Central atom: Sulfur (S)
- Valence electrons: Sulfur has 6 valence electrons.
- Lewis structure: Sulfur forms bonds with 2 oxygen atoms and 1 fluorine atom using all its electrons, leaving no lone pairs.
- Lone pairs: 0 lone pairs on the central sulfur atom.

### Conclusion:
The compounds that contain 2 lone pairs of electrons on the central atom are:
- I3⁻ (Iodine triiodide ion)
- H2O (Water)
- XeF4 (Xenon tetrafluoride)
- H2S (Hydrogen sulfide)

### Final Answer:
The pairs that contain 2 lone pairs of electrons on the central atom are I3⁻, H2O, XeF4, and H2S.