Question

Identify the correct order of thermal stability of hydrides of 16 group elements from the following.

• A. \(\text{H}_2\text{S}<\text{H}_2\text{O}<\text{H}_2\text{Se}<\text{H}_2\text{Te}\)
• B. \(\text{H}_2\text{O}<\text{H}_2\text{S}<\text{H}_2\text{Se}<\text{H}_2\text{Te}\)
• C. \(\text{H}_2\text{Te}<\text{H}_2\text{Se}<\text{H}_2\text{S}<\text{H}_2\text{O}\)
• D. \(\text{H}_2\text{Se}<\text{H}_2\text{Te}<\text{H}_2\text{O}<\text{H}_2\text{S}\)

Hint:

Down the group: bond length ↑ → bond strength ↓ → stability ↓.

Answer 1

The Correct Option is C

Concept:
Thermal stability of hydrides depends on the bond strength of E–H bond (E = group 16 element). Stronger the bond → higher the thermal stability. Step 1: Understand the trend in group 16. Group 16 elements: \[ \text{O} \rightarrow \text{S} \rightarrow \text{Se} \rightarrow \text{Te} \] As we move down the group:

• Atomic size increases
• Bond length increases
• Bond strength decreases

Step 2: Effect on E–H bond. \[ \text{O–H}>\text{S–H}>\text{Se–H}>\text{Te–H} \] So, thermal stability follows the same order.
Step 3: Write correct stability order. \[ \text{H}_2\text{O}>\text{H}_2\text{S}>\text{H}_2\text{Se}>\text{H}_2\text{Te} \]
Step 4: Match with options. Since options are in increasing order: \[ \text{H}_2\text{Te}<\text{H}_2\text{Se}<\text{H}_2\text{S}<\text{H}_2\text{O} \]
Step 5: Conclusion. Correct option is (C).