The correct order of stability of hydrides of alkali metals is

Options

A. `NaHgtLiHgtKHgtRbHgtCsH`
B. `LiHgtNaHgtKHgtRbHgtCsH`
C. `CsHgtRbHgtKHgtNaHgtLiH`
D. `KHgtNaHgtLiHgtcsHgtRbH`

Explanation

To determine the correct order of stability of hydrides of alkali metals, we need to analyze the factors affecting the stability of these hydrides. Here's a step-by-step solution:

### Step 1: Identify the Alkali Metals
The alkali metals are lithium (Li), sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs). Their corresponding hydrides are lithium hydride (LiH), sodium hydride (NaH), potassium hydride (KH), rubidium hydride (RbH), and cesium hydride (CsH).

### Step 2: Understand Stability of Hydrides
The stability of hydrides of alkali metals generally decreases down the group. This is primarily due to the increase in the size of the alkali metal cations as we move from Li to Cs.

### Step 3: Analyze Ionic Size
As we move down the group from lithium to cesium, the size of the alkali metal ions increases:
- Li⁺ < Na⁺ < K⁺ < Rb⁺ < Cs⁺

### Step 4: Consider Hydride Ion Size
The hydride ion (H⁻) is relatively small. The stability of the hydride is greater when it forms a bond with a smaller cation. Therefore, a smaller cation will lead to a more stable hydride.

### Step 5: Establish the Order of Stability
Since Li⁺ is the smallest cation, LiH is the most stable hydride. As the size of the cation increases, the stability of the hydride decreases. Thus, the order of stability of the hydrides is:
- LiH > NaH > KH > RbH > CsH

### Step 6: Final Answer
The correct order of stability of hydrides of alkali metals is:
**LiH > NaH > KH > RbH > CsH**