To analyze the assertion and reason provided in the question, we will break down the statements and evaluate their validity step by step.
### Step 1: Evaluate the Assertion (A)
**Assertion (A): Alkali metals form ionic hydrides which contain hydride ions.**
- **Explanation**: Alkali metals (Group 1 elements) such as lithium (Li), sodium (Na), and potassium (K) readily react with hydrogen to form hydrides. These hydrides are ionic in nature because alkali metals are highly electropositive and tend to lose their outermost electron easily. When they react with hydrogen, they form compounds that contain the hydride ion (H⁻). For example, lithium hydride (LiH), sodium hydride (NaH), and potassium hydride (KH) are all ionic hydrides containing the hydride ion.
- **Conclusion**: The assertion is **true**.
### Step 2: Evaluate the Reason (R)
**Reason (R): The alkali metals have low electronegativity. Their hydrides conduct electricity when fused and liberate hydrogen at the anode.**
- **Explanation**: Alkali metals have low electronegativity due to their large atomic size. As the size of the alkali metal increases, the attraction between the nucleus and the outermost electron decreases, making it easier for these metals to lose their electrons. This low electronegativity is a characteristic of alkali metals, which contributes to their ability to form ionic compounds.
- **Conductivity**: The hydrides of alkali metals are ionic and, when fused, they dissociate into their respective ions (e.g., Li⁺ and H⁻ for lithium hydride). This ionic nature allows them to conduct electricity when in a molten state. During electrolysis, the hydride ions (H⁻) can lose electrons at the anode, resulting in the liberation of hydrogen gas.
- **Conclusion**: The reason is also **true** and provides a valid explanation for the assertion.
### Step 3: Determine the Relationship
Since both the assertion and the reason are true, and the reason correctly explains why the assertion is true, we can conclude that:
- **Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation for Assertion (A).**
### Final Answer
The correct option is that both statements are true, and the reason is the correct explanation for the assertion.
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