Which of the following compounds is covalent ? .

Options

A. `H_(2)`
B. `CaO`
C. `KCI`
D. `Na_(2)S`

Explanation

To determine which of the given compounds is covalent, we need to analyze each compound based on the type of bonding it exhibits. Covalent bonds are formed when two atoms share electrons, typically between nonmetals, while ionic bonds are formed through the transfer of electrons from one atom to another, typically between metals and nonmetals.

### Step-by-Step Solution:

1. **Analyze Compound A: Hydrogen (H₂)**
- Hydrogen exists as a diatomic molecule (H₂).
- In H₂, two hydrogen atoms share a pair of electrons, forming a single covalent bond.
- **Conclusion:** H₂ is a covalent compound.

2. **Analyze Compound B: Calcium Oxide (CaO)**
- Calcium oxide consists of calcium ions (Ca²⁺) and oxide ions (O²⁻).
- The bond between Ca²⁺ and O²⁻ is formed through the transfer of electrons from calcium to oxygen, resulting in ionic bonding.
- **Conclusion:** CaO is an ionic compound.

3. **Analyze Compound C: Potassium Chloride (KCl)**
- Potassium chloride consists of potassium ions (K⁺) and chloride ions (Cl⁻).
- Similar to CaO, KCl is formed through the transfer of electrons from potassium to chlorine, resulting in ionic bonding.
- **Conclusion:** KCl is an ionic compound.

4. **Analyze Compound D: Sodium Sulfide (Na₂S)**
- Sodium sulfide consists of sodium ions (Na⁺) and sulfide ions (S²⁻).
- The bonding in Na₂S also involves the transfer of electrons from sodium to sulfur, leading to ionic bonding.
- **Conclusion:** Na₂S is an ionic compound.

### Final Answer:
The only covalent compound among the options provided is **A: Hydrogen (H₂)**.