A polar covalent bond will be formed in which one of these pair of atoms:

Options

A. HF
B. `H_2`
C. `Cl_2`
D. `O_2`

Explanation

To determine which pair of atoms forms a polar covalent bond, we need to analyze the electronegativity of the atoms involved and their ability to share electrons. Let's break down the steps:

### Step 1: Understand Polar Covalent Bonds
A polar covalent bond occurs when two atoms share electrons unequally due to a difference in their electronegativities. The atom with higher electronegativity attracts the shared electrons more strongly, resulting in partial positive and negative charges.

### Step 2: Identify the Pairs of Atoms
The question provides several pairs of atoms. Let's consider them:
1. HF (Hydrogen Fluoride)
2. H2 (Hydrogen)
3. Cl2 (Chlorine)
4. O2 (Oxygen)

### Step 3: Determine the Electronegativity of Each Atom
- **Hydrogen (H)** has an electronegativity of about 2.1.
- **Fluorine (F)** has an electronegativity of about 4.0.
- **Chlorine (Cl)** has an electronegativity of about 3.0.
- **Oxygen (O)** has an electronegativity of about 3.5.

### Step 4: Analyze Each Pair
1. **HF**: The electronegativity difference is |4.0 - 2.1| = 1.9. This significant difference indicates a polar covalent bond.
2. **H2**: Both atoms are hydrogen, so the electronegativity difference is 0. This means it is a non-polar covalent bond.
3. **Cl2**: Both atoms are chlorine, so the electronegativity difference is 0. This means it is a non-polar covalent bond.
4. **O2**: Both atoms are oxygen, so the electronegativity difference is 0. This means it is a non-polar covalent bond.

### Step 5: Conclusion
The only pair that forms a polar covalent bond is **HF** (Hydrogen Fluoride) due to the significant difference in electronegativity between hydrogen and fluorine.

### Final Answer
**HF (Hydrogen Fluoride)** is the pair of atoms that forms a polar covalent bond.

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