Which among `Na,K,Cs` and `Li` forms most stable hydride?

Options

A. Lii l
B. KH
C. NaH
D. CsH

Answer

To determine which among Na, K, Cs, and Li forms the most stable hydride, we can follow these steps:

### Step 1: Understand the Alkali Metals and Their Hydrides
- The alkali metals in question are lithium (Li), sodium (Na), potassium (K), and cesium (Cs).
- Each of these metals forms a hydride: lithium hydride (LiH), sodium hydride (NaH), potassium hydride (KH), and cesium hydride (CsH).

### Step 2: Reactivity of Alkali Metals
- Alkali metals are known to have increasing reactivity as we move down the group in the periodic table.
- The order of reactivity for these metals is: Cs > K > Na > Li.
- This means that lithium is the least reactive of the four metals.

### Step 3: Stability of Hydrides
- The stability of a hydride is generally inversely related to the reactivity of the corresponding alkali metal.
- Therefore, the less reactive the metal, the more stable its hydride will be.

### Step 4: Compare the Hydrides
- Since lithium is the least reactive, lithium hydride (LiH) will be the most stable among the hydrides formed by these metals.
- Conversely, cesium, being the most reactive, will have the least stable hydride (CsH).

### Conclusion
- Based on the reactivity and stability relationship, the most stable hydride among Na, K, Cs, and Li is lithium hydride (LiH).

### Final Answer
- **LiH (lithium hydride) is the most stable hydride.**

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