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Formal charge on oxygen = -3/4 = -0.75

1. We know that due to polar nature, water molecules are held together by intermolecular hydrogen bonds. The structure of ice is open with large number of vacant spaces, therefore the density of ice is less than water.
2. The b.p. of p-nitrophenol is higher than that of o-nitrophenol because in p-nitrophenol there is intermolecular H-bonding but in o-nitrophenol it is intramolecular H-bonding.
3. Intramolecular Hydrogen bonding in o-nitrophenol is a interaction within the molecule whereas the intermolecular H-bonding in p-nitrophenol is a interaction between the molecules which results into higher boiling point. Intermolecular hydrogen bonding also results in a stronger driving force for crystal formation in other molecules generating higher melting temperature e.g. p-hydroxy benzoic acid.
4. The strength of the interactions follows the order: van der Waal’s < hydrogen bonding < dipole-dipole < covalent.

Correct answer: The b.p. of p-nitrophenol is higher than that of o-nitrophenol because in p-nitrophenol there is intermolecular H-bonding but in o-nitrophenol it is intramolecular H-bonding.

Solution

Option B is correct because the boiling point of p-nitrophenol is higher due to intermolecular hydrogen bonding, which is stronger and requires more energy to break compared to the intramolecular hydrogen bonding in o-nitrophenol.

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