Among the hydrides formed by the group VI-A elements, only `H_2 O` has an abnormally low volatility (high boiling point). This is so because

Options

A. `H_(2)O` molecules are associated due to intermolecular hydrogen bond
B. `H_(2)O` is covalent in nature
C. The O-H bond in `H_(2)O` is very strong
D. The electronegativity difference of H and O is very large

Answer

To understand why water (H₂O) has an abnormally low volatility (high boiling point) compared to other hydrides formed by group VI-A elements, we can break down the explanation into several steps:

### Step 1: Identify the Hydrides of Group VI-A Elements
The hydrides formed by group VI-A elements (chalcogens) include:
- H₂O (water)
- H₂S (hydrogen sulfide)
- H₂Se (hydrogen selenide)
- H₂Te (hydrogen telluride)

### Step 2: Compare the Boiling Points
The boiling points of these hydrides show a trend:
- H₂O: 100 °C
- H₂S: -60 °C
- H₂Se: -41 °C
- H₂Te: -2 °C

From this, we can see that H₂O has a significantly higher boiling point than the other hydrides.

### Step 3: Understand the Role of Hydrogen Bonding
The key reason for the high boiling point of H₂O is the presence of hydrogen bonding. Hydrogen bonds are strong intermolecular forces that occur when hydrogen is bonded to highly electronegative atoms like oxygen. In water:
- Each water molecule can form hydrogen bonds with neighboring water molecules due to the polarity of the O-H bond.
- The oxygen atom is more electronegative than hydrogen, creating a dipole moment.

### Step 4: Analyze the Intermolecular Forces
In contrast, the other hydrides (H₂S, H₂Se, H₂Te) do not exhibit significant hydrogen bonding because:
- Sulfur, selenium, and tellurium are less electronegative than oxygen, resulting in weaker dipole moments.
- The intermolecular forces in these hydrides are primarily Van der Waals forces, which are much weaker than hydrogen bonds.

### Step 5: Conclusion
The presence of strong hydrogen bonds in water leads to a higher boiling point compared to the other hydrides formed by group VI-A elements. This is the primary reason why H₂O has an abnormally low volatility (high boiling point).

### Final Answer
Among the hydrides formed by the group VI-A elements, only H₂O has an abnormally low volatility (high boiling point) because it forms strong hydrogen bonds due to the high electronegativity of oxygen, which is not the case for the other hydrides.

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