Among `CaH_2, NH_3, NaH` and `B_2H_6` which are covalent hydrides?

Options

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

Explanation

To determine which of the given compounds are covalent hydrides among CaH₂, NH₃, NaH, and B₂H₆, we can analyze the nature of bonding in each compound.

### Step 1: Identify the elements in each compound
- **CaH₂**: Contains Calcium (Ca) and Hydrogen (H).
- **NH₃**: Contains Nitrogen (N) and Hydrogen (H).
- **NaH**: Contains Sodium (Na) and Hydrogen (H).
- **B₂H₆**: Contains Boron (B) and Hydrogen (H).

### Step 2: Classify the elements
- **Calcium (Ca)** and **Sodium (Na)** are metals (alkaline earth metal and alkali metal, respectively).
- **Nitrogen (N)** and **Boron (B)** are non-metals.

### Step 3: Determine the type of hydride formed
- **Ionic Hydrides**: Typically formed by metals with hydrogen. They usually have a high electronegativity difference between the metal and hydrogen, leading to ionic bonding.
- **CaH₂**: Calcium is a metal, so it forms an ionic hydride.
- **NaH**: Sodium is also a metal, so it forms an ionic hydride.

- **Covalent Hydrides**: Formed by non-metals that have similar electronegativities, leading to covalent bonding.
- **NH₃**: Nitrogen is a non-metal, and it forms a covalent hydride.
- **B₂H₆**: Boron is a non-metal, and it also forms a covalent hydride.

### Step 4: Conclusion
From the analysis:
- **Covalent Hydrides**: NH₃ and B₂H₆
- **Ionic Hydrides**: CaH₂ and NaH

Thus, the covalent hydrides among the given options are **NH₃ and B₂H₆**.

### Final Answer
The covalent hydrides among the given compounds are **NH₃ and B₂H₆**.

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