Answer
Liquid HF has intermolecular hydrogen bonding whereas liquid HI does not have intermolecular hydrogen bonding. Hence, liquid HI has very weak intermolecular forces compared to liquid HF. As the strength of intermolecular forces decreases, vapor pressure increases. So liquid HI has a higher vapor pressure than liquid HF at $-35^{\circ}C$.
Work Step by Step
Liquid HF has intermolecular hydrogen bonding whereas liquid HI does not have intermolecular hydrogen bonding. Hence, liquid HI has very weak intermolecular forces compared to liquid HF. As the strength of intermolecular forces decreases, vapor pressure increases. So liquid HI has a higher vapor pressure than liquid HF at $-35^{\circ}C$.
