4t room temperature and pressure, \( \mathrm{H}_{2} \mathrm{O} \) is a liquid and \( \mathrm{H}_{2} \mathrm{~S} \) is a gas. s futes of matter is What is the reason for this difference? A O has higher first and second ionisation energies than S . B The covalent bond between O and H is stronger than the covalent bond between S and H . C There is significant hydrogen bonding between \( \mathrm{H}_{2} \mathrm{O} \) molecules but not between \( \mathrm{H}_{2} \mathrm{~S} \) molecules. D The instantaneous dipole-induced dipole forces between \( \mathrm{H}_{2} \mathrm{O} \) molecules are stronger than the instantaneous dipole-induced dipole forces between \( \mathrm{H}_{2} \mathrm{~S} \) molecules.

1. Identify the molecular properties of \(\mathrm{H}_2\mathrm{O}\) and \(\mathrm{H}_2\mathrm{S}\). - In \(\mathrm{H}_2\mathrm{O}\), oxygen is highly electronegative, and the molecule has a bent shape, which creates a significant dipole moment. - In \(\mathrm{H}_2\mathrm{S}\), sulfur is less electronegative than oxygen and the molecule has a less polar character. 2. Consider the intermolecular forces present in both substances. - \(\mathrm{H}_2\mathrm{O}\) experiences hydrogen bonding because the highly electronegative oxygen can attract hydrogen atoms from neighboring \(\mathrm{H}_2\mathrm{O}\) molecules. - \(\mathrm{H}_2\mathrm{S}\) does not exhibit significant hydrogen bonding because sulfur is not sufficiently electronegative; instead, its primary intermolecular forces are weak London dispersion forces. 3. Evaluate the given options: - **Option A:** Discusses ionisation energies, which are not directly related to the intermolecular forces responsible for physical state. - **Option B:** Refers to the strength of the covalent bond within molecules; however, the physical state is influenced by intermolecular forces, not intramolecular bonding. - **Option C:** Correctly identifies the presence of significant hydrogen bonding in \(\mathrm{H}_2\mathrm{O}\) compared to the absence of such bonding in \(\mathrm{H}_2\mathrm{S}\). - **Option D:** Mentions instantaneous dipole-induced dipole forces, which are not the main intermolecular force in \(\mathrm{H}_2\mathrm{O}\). 4. Conclude the reason: The difference in physical states at room temperature is due to the strong hydrogen bonding between \(\mathrm{H}_2\mathrm{O}\) molecules, which leads to higher boiling and melting points, making water a liquid. In contrast, the weaker London dispersion forces in \(\mathrm{H}_2\mathrm{S}\) allow it to be a gas. Thus, the correct answer is: \( \boxed{C} \)