Among `CaH_(2),NH_(3),` and `B_(2)H_(6)` which are covalent hydrides?

Options

A. `NH_(3) and B_(2)H_(6)`
B. `NaH and CaH_(2)`
C. `NaH and NH_(3)`
D. `CaH_(2) and B_(2)H_(6)`

Answer

To determine which of the given compounds \( CaH_2 \), \( NH_3 \), and \( B_2H_6 \) are covalent hydrides, we can follow these steps:

### Step 1: Understand the Types of Hydrides
Hydrides can be classified into two main categories: ionic hydrides and covalent hydrides.
- **Ionic hydrides** are typically formed by elements from the s-block of the periodic table (alkali and alkaline earth metals) and contain hydrogen in the form of H⁻ ions.
- **Covalent hydrides** are generally formed by p-block elements and involve sharing of electrons between the hydrogen and the other element.

### Step 2: Analyze Each Compound
1. **\( CaH_2 \)**:
- Calcium (Ca) is an alkaline earth metal (s-block).
- It forms ionic bonds with hydrogen, leading to the formation of \( CaH_2 \) as an ionic hydride.

2. **\( NH_3 \)**:
- Nitrogen (N) is a p-block element.
- In ammonia, nitrogen shares electrons with hydrogen, forming covalent bonds. Therefore, \( NH_3 \) is a covalent hydride.

3. **\( B_2H_6 \)**:
- Boron (B) is also a p-block element.
- The bonding in \( B_2H_6 \) involves covalent bonds between boron and hydrogen. Thus, \( B_2H_6 \) is a covalent hydride.

### Step 3: Conclusion
Based on the analysis:
- \( CaH_2 \) is an ionic hydride.
- \( NH_3 \) and \( B_2H_6 \) are covalent hydrides.

Thus, the covalent hydrides among the given options are \( NH_3 \) and \( B_2H_6 \).

### Final Answer
The covalent hydrides are \( NH_3 \) and \( B_2H_6 \).

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