6. H₂O is a liquid whereas H₂S is a gas at 25⁰C. The reason for this is

   (1) the number of electrons in the outermost electron shells of oxygen and sulfur are different.
   (2) lack of hydrogen bonds in H₂O.
   (3) the hydrogen-sulfur bond is more polar than the hydrogen-oxygen bond.
   (4) lack of hydrogen bonds in H₂S.

Why is H₂O a Liquid and H₂S a Gas at 25°C?

Water (H2O) is a liquid at room temperature (25°C), but hydrogen sulphide (H2S) is a gas. The main cause of this physical state difference is hydrogen bonding, which has a big impact on intermolecular forces and boiling points.

Knowing the Main Distinction: Hydrogen Bonding

Option 4—the absence of hydrogen bonds in H₂S—is the proper explanation for this behaviour.

Because oxygen has a high electronegativity, H2O forms strong hydrogen bonds.

Up to four hydrogen bonds can be formed between adjacent molecules and each water molecule.

Water becomes a liquid at room temperature due to the strong intermolecular forces that raise the boiling point.

Since sulphur is less electronegative than oxygen, H₂S does not form hydrogen bonds.

Intermolecular attraction is reduced in H₂S due to the weaker dipole interactions.

Because of its low boiling point, H₂S is a gas at 25°C.

Why the Other Choices Are Wrong

Option 1: Sulphur and oxygen have different numbers of electrons

Despite being in the same group (Group 16), sulphur and oxygen share the same valence electrons (6). The physical state difference is unaffected by this.

Option 2: H2O does not contain hydrogen bonds

This is untrue because water’s liquid state is largely dependent on hydrogen bonds.

Option 3: The hydrogen-sulfur bond is more polar than the hydrogen-oxygen bond.

Because of the higher electronegativity of oxygen, the H-O bond is actually more polar than the H-S bond.

Conclusion: Hydrogen Bonding’s Function

The absence of hydrogen bonding in H₂S is the main cause of H₂O being a liquid and H₂S being a gas at room temperature. Under normal circumstances, water’s higher boiling points and strong hydrogen bonding make it a liquid, but H₂S’s weaker intermolecular forces allow it to stay a gas.

Since hydrogen bonds affect everything from the behaviour of biomolecules to the special qualities of water, an understanding of them is essential in chemistry, biology, and environmental science.