The most acidic and thermally stable hydride of chalcogens are respectively 

Options

A. `H_(2)O, H_(2)Te`
B. `H_(2)Te, H_(2)S`
C. `H_(2)S, H_(2)Te`
D. `H_(2)Te, H_(2)O`

Answer

To solve the question about the most acidic and thermally stable hydride of chalcogens, we need to analyze the hydrides of the group 16 elements: oxygen, sulfur, selenium, and tellurium.

### Step-by-Step Solution:

1. **Identify the Hydrides**:
- The hydrides of chalcogens are:
- H2O (water) for oxygen
- H2S (hydrogen sulfide) for sulfur
- H2Se (hydrogen selenide) for selenium
- H2Te (hydrogen telluride) for tellurium

2. **Determine Thermal Stability**:
- As we move down the group from oxygen to tellurium, the atomic size increases.
- This increase in atomic size leads to an increase in the bond length of the M-H bond (where M is the chalcogen).
- A longer bond length typically results in a weaker bond. Therefore, the thermal stability of the hydrides decreases down the group.
- Thus, the order of thermal stability is:
- H2O > H2S > H2Se > H2Te
- Therefore, the most thermally stable hydride is **H2O**.

3. **Determine Acidity**:
- Acidity in this context refers to the ability of the hydride to donate H+ ions.
- As we move down the group, the M-H bond becomes weaker, which means it is easier for the hydride to release H+ ions.
- Therefore, the acidic strength increases down the group:
- H2Te > H2Se > H2S > H2O
- Consequently, the most acidic hydride is **H2Te**.

4. **Final Conclusion**:
- The most acidic hydride is **H2Te** and the most thermally stable hydride is **H2O**.
- Therefore, the answer to the question is: **H2Te (most acidic) and H2O (most thermally stable)**.

### Summary:
- Most acidic hydride: **H2Te**
- Most thermally stable hydride: **H2O**