The effect of repulsion between the two lone pairs of electrons present on oxygen in `H_(2)O` molecule is

Options

A. no change in `H-O-H` bond angle
B. increase in `H-O-H` bond angle
C. decrease in `H-O-H` bond angle
D. all atoms will be in one plane

Answer

To solve the question regarding the effect of repulsion between the two lone pairs of electrons present on oxygen in the H₂O molecule, we can follow these steps:

### Step 1: Understand the Structure of H₂O
- The water molecule (H₂O) consists of one oxygen atom bonded to two hydrogen atoms.
- The oxygen atom has two lone pairs of electrons in addition to the two bond pairs formed with hydrogen.

**Hint:** Recall the basic structure of water and the number of lone pairs and bond pairs on the central atom (oxygen).

### Step 2: Identify the Expected Bond Angle
- In a tetrahedral arrangement (which is the ideal geometry for four electron pairs), the bond angle is expected to be approximately 109.5 degrees.
- However, in H₂O, we have two lone pairs and two bond pairs, which alters the geometry.

**Hint:** Consider the ideal bond angles in tetrahedral geometry and how lone pairs affect these angles.

### Step 3: Analyze the Effect of Lone Pair Repulsion
- Lone pairs of electrons occupy more space than bonding pairs because they are only associated with one nucleus (the oxygen atom).
- The repulsion between the two lone pairs is stronger than the repulsion between the bonding pairs (H-O bonds).
- This stronger repulsion pushes the hydrogen atoms closer together, reducing the bond angle.

**Hint:** Think about how lone pairs influence the spatial arrangement of atoms in a molecule.

### Step 4: Determine the Actual Bond Angle
- Due to the repulsion from the lone pairs, the actual bond angle (H-O-H) in water is approximately 104.5 degrees, which is less than the expected 109.5 degrees.

**Hint:** Recall the actual bond angle in H₂O and how it compares to the ideal bond angle.

### Step 5: Conclusion
- The effect of repulsion between the two lone pairs of electrons on the oxygen atom in the H₂O molecule results in a decrease in the H-O-H bond angle.

**Final Answer:** The correct option is "decrease in H-O-H bond angle."

### Summary of Steps:
1. Understand the structure of H₂O.
2. Identify the expected bond angle.
3. Analyze the effect of lone pair repulsion.
4. Determine the actual bond angle.
5. Conclude the effect of repulsion.