Which of the following hydrides are non-stoichiometric?

Options

A. Saline
B. Metallic
C. Molecular
D. Polymeric

Answer

To determine which of the given hydrides are non-stoichiometric, we need to analyze the options provided: saline hydrides, metallic hydrides, molecular hydrides, and polymeric hydrides.

### Step-by-Step Solution:

1. **Understanding Non-Stoichiometric Hydrides**:
- Non-stoichiometric hydrides are those that do not have a fixed ratio of hydrogen to metal atoms. This typically occurs in certain types of hydrides formed with transition metals.

2. **Analyzing the Options**:
- **Saline Hydrides**: These are formed with alkali and alkaline earth metals (e.g., NaH, CaH2). They have a fixed stoichiometry (1:1 or 1:2) and are not non-stoichiometric.
- **Metallic Hydrides**: These are formed with transition metals and can have varying amounts of hydrogen, leading to non-stoichiometric compositions. For example, in metallic hydrides, hydrogen occupies interstitial sites in the metal lattice, which means the ratio of hydrogen to metal can vary.
- **Molecular Hydrides**: These typically consist of covalent compounds (e.g., CH4, NH3) and have a definite stoichiometric ratio.
- **Polymeric Hydrides**: These are also likely to have a defined structure and stoichiometry.

3. **Conclusion**:
- From the analysis, it is clear that **metallic hydrides** are the ones that are non-stoichiometric due to their ability to accommodate varying amounts of hydrogen in their structure.

### Final Answer:
The non-stoichiometric hydrides among the options provided are **metallic hydrides** (Option B).

---