At 298 K and 1 atm, bromine is a liquid with a high vapor pressure, whereas chlorine is a gas. This — Bonding Chemistry Question

STEPS:

1. Analyze the Physical States: The question notes that at room temperature ($298\text{ K}$) and standard pressure ($1\text{ atm}$), bromine ($Br_2$) is a liquid while chlorine ($Cl_2$) is a gas.
2. Identify the Relevant Force: The physical state of a molecular substance—whether it is a solid, liquid, or gas—is determined by the strength of the attractions between molecules, known as intermolecular forces (IMFs).
3. Relate IMFs to Phase: In a gas, the kinetic energy of the molecules is high enough to overcome the attractive forces between them, allowing them to move far apart. In a liquid, the IMFs are strong enough to keep the molecules in close contact.
4. Compare the Substances: Since bromine exists as a liquid under the same conditions that chlorine exists as a gas, it must be because the forces among $Br_2$ molecules are stronger than the forces among $Cl_2$ molecules.
5. Determine the specific IMF type: Both $Cl_2$ and $Br_2$ are nonpolar, diatomic molecules that only experience London Dispersion Forces (LDFs). Because bromine atoms are larger and have more electrons than chlorine atoms, the $Br_2$ molecule has a larger, more polarizable electron cloud, resulting in stronger LDFs.
6. Conclusion: The observation that $Br_2$ is a liquid while $Cl_2$ is a gas provides direct evidence that the intermolecular attractions in bromine are greater than those in chlorine, which matches Option A.

WHY_OTHERS_WRONG:

• B and C: These options compare intermolecular forces (attractions between molecules) to intramolecular covalent bonds (the $Br\text{--}Br$ or $Cl\text{--}Cl$ bond within the molecule). Covalent bonds are typically much stronger than IMFs; however, the state of matter at room temperature is governed by the strength of the attractions *between* separate molecules, not the bonds holding the individual atoms together.
• D and E: These options discuss the strength of the covalent bonds within the molecules. While bond strength is critical for determining chemical stability and reaction enthalpy, it does not dictate the physical state (gas, liquid, or solid) of a molecular substance at a given temperature and pressure.