The boiling point of $p$-nitrophenol is higher than that of $o$-nitrophenol because:

• A
  $p$-nitrophenol has intermolecular hydrogen bonding and $o$-nitrophenol has intramolecular hydrogen bonding.
• B
  $p$-nitrophenol has intramolecular hydrogen bonding and $o$-nitrophenol has intermolecular hydrogen bonding.
• C
  $p$-nitrophenol is polar while $o$-nitrophenol is non-polar.
• D
  Van der Waals forces are stronger in $o$-nitrophenol.