Boric acid is a solid at room temperature due to the presence of strong hydrogen bonding between its molecules. In contrast, boron trifluoride (\( BF_3 \)) is a gas at room temperature because it is a simple covalent molecule with weak van der Waals forces and no hydrogen bonding capabilities.
Understanding Boric Acid and Its Interactions:
Boric acid (\( \text{H}_3\text{BO}_3 \)) is a weak monobasic Lewis acid of boron.
It has the capability to form strong hydrogen bonds due to the presence of hydroxyl groups (-OH) that can donate and accept hydrogen bonds with neighboring molecules.
This extensive hydrogen bonding network grants boric acid a higher melting point, making it solid at room temperature.
Understanding Boron Trifluoride and Its Interactions:
Boron trifluoride (\( BF_3 \)) is a planar molecule with boron surrounded by three fluorine atoms.
Due to its small size and lack of hydrogen bonding capability, \( BF_3 \) relies primarily on weak van der Waals forces.
The weak intermolecular forces lead to it being a gas at room temperature.
Eliminating Incorrect Options:
Strong van der Waal's interaction assumes that both molecules would behave similarly, which is not the case between a gas and a solid under the same conditions.
Strong covalent bonds in \( BF_3 \) are intramolecular, affecting the internal structure rather than phase state.
Strong ionic bonds in boric acid imply ionic character, which is not observed as boric acid primarily involves covalent bonding.
Conclusion:
The correct explanation for the phase differences is the presence of strong hydrogen bonds in boric acid, which result in it being a solid at room temperature. Thus, the correct answer is:
