To solve the assertion-reason question regarding the thermal stability of \( H_2O \) compared to \( H_2S \), we will analyze both the assertion and the reason step by step.
### Step 1: Analyze the Assertion
**Assertion (A)**: \( H_2O \) is thermally more stable than \( H_2S \).
- **Explanation**: The thermal stability of a molecule is influenced by the strength of the bonds present in it. In \( H_2O \), the bond is an O-H bond, while in \( H_2S \), the bond is an S-H bond.
- **Bond Strength**: The O-H bond is stronger than the S-H bond due to the smaller size of the oxygen atom compared to sulfur. This results in a shorter bond length for O-H, which correlates with greater bond strength.
- **Conclusion**: Since \( H_2O \) has stronger bonds than \( H_2S \), it is indeed thermally more stable. Therefore, the assertion is **True**.
### Step 2: Analyze the Reason
**Reason (R)**: \( H_2O \) molecules can form intermolecular hydrogen bonds whereas \( H_2S \) molecules cannot.
- **Explanation**: Hydrogen bonding occurs when hydrogen is bonded to highly electronegative atoms such as fluorine, oxygen, or nitrogen. In \( H_2O \), hydrogen is bonded to oxygen, which is highly electronegative, allowing for hydrogen bonding between molecules.
- **Comparison with \( H_2S \)**: In \( H_2S \), hydrogen is bonded to sulfur, which is less electronegative than oxygen. As a result, \( H_2S \) cannot form significant hydrogen bonds.
- **Conclusion**: The reason provided is **True** as \( H_2O \) can form hydrogen bonds while \( H_2S \) cannot.
### Step 3: Determine the Relationship Between Assertion and Reason
- While both the assertion and the reason are true, the reason does not directly explain why \( H_2O \) is thermally more stable than \( H_2S \). The thermal stability is primarily due to bond strength and bond length, not hydrogen bonding.
### Final Conclusion
Both the assertion and the reason are true, but the reason is not the correct explanation for the assertion. Therefore, the answer is that both A and R are true, but R is not the correct explanation of A.
