If the intermolecular forces are large enough, the measured pressure p of a gas that obeys the van der Waals equation of state could be zero. (a) For what value of the volume per mole would this occur? (Hint: There are two solutions; find them both and interpret them.) (b) Show that there is a maximum temperature for zero pressure to occur, and find this maximum temperature in terms of the a and b parameters in the van der Waals equation. (c) Assuming that oxygen obeys the van der Waals equation with a=0.138 J m³/mol² and b=3.18 times10⁻⁵ m³/mol, find the maximum temperature for which p=0 for oxygen and compare this value with the normal boiling point of oxygen.