In case of hydride of oxyge family, which of the following physical property change regularly on moving down the group

Options

A. Melting point
B. Thermal stability
C. Boiling point
D. Critical temperature

Explanation

To determine which physical property of the hydrides of the oxygen family changes regularly as we move down the group, we can analyze the properties of the hydrides: H₂O (water), H₂S (hydrogen sulfide), H₂Se (hydrogen selenide), and H₂Te (hydrogen telluride).

### Step-by-Step Solution:

1. **Identify the Hydrides**:
The hydrides of the oxygen family (Group 16) include:
- H₂O (water)
- H₂S (hydrogen sulfide)
- H₂Se (hydrogen selenide)
- H₂Te (hydrogen telluride)

2. **List the Properties to Analyze**:
The properties we need to consider are:
- Melting point
- Boiling point
- Critical temperature
- Thermal stability

3. **Analyze Melting Point, Boiling Point, and Critical Temperature**:
- These properties are influenced by intermolecular forces.
- As we move down the group, the molecular weight increases, leading to stronger van der Waals forces due to increased polarizability.
- However, H₂O exhibits strong hydrogen bonding, which is a significant factor in its physical properties, making it an exception.
- The trend for these properties (excluding H₂O) generally increases down the group: H₂Te > H₂Se > H₂S > H₂O.

4. **Analyze Thermal Stability**:
- Thermal stability refers to the stability of the bonds in the hydrides.
- As we move down the group, the bond strength decreases due to the increasing size of the atoms, which leads to weaker bonds.
- Therefore, the thermal stability decreases down the group: H₂O > H₂S > H₂Se > H₂Te.

5. **Conclusion**:
- Among the properties analyzed, the one that changes regularly down the group is thermal stability, as it consistently decreases due to the weakening of the bonds in the hydrides.

### Final Answer:
The physical property that changes regularly on moving down the group in the hydrides of the oxygen family is **thermal stability**.