The correct order of the thermal stability of hydrogen halides `(H-X)` is

Options

A. `HlgtHbegtHClgtHF`
B. `HFgtHClgtHBrgtHI`
C. `HClltHFltHBrltHI`
D. `HIgtHClgtHFltHBr`

Explanation

To determine the correct order of thermal stability of hydrogen halides (H-X), we need to analyze the bond strength of the H-X bonds. The thermal stability of these compounds is influenced by the strength of the bond between hydrogen and the halogen (X).

### Step-by-Step Solution:

1. **Understanding Thermal Stability**:
- Thermal stability refers to the ability of a compound to resist decomposition at elevated temperatures. For hydrogen halides, this stability is primarily determined by the strength of the H-X bond.

2. **Bond Strength and Bond Length**:
- The strength of the H-X bond is inversely related to the bond length. A shorter bond length typically indicates a stronger bond. Conversely, a longer bond length indicates a weaker bond.

3. **Analyzing the Halogens**:
- The halogens (F, Cl, Br, I) increase in size as we move down the group in the periodic table:
- Fluorine (F) is the smallest, followed by chlorine (Cl), bromine (Br), and iodine (I), which is the largest.

4. **Bond Length Trends**:
- As the size of the halogen increases, the bond length of the H-X bond also increases:
- H-F < H-Cl < H-Br < H-I
- This means that H-I has the longest bond length and therefore the weakest bond strength.

5. **Bond Strength Trends**:
- Since bond strength decreases with increasing bond length, we can establish the following order of bond strengths:
- H-F > H-Cl > H-Br > H-I

6. **Thermal Stability Order**:
- Since thermal stability is directly related to bond strength, the order of thermal stability for hydrogen halides is:
- H-F > H-Cl > H-Br > H-I

### Final Answer:
The correct order of thermal stability of hydrogen halides (H-X) is:
**H-F > H-Cl > H-Br > H-I**