Maximum vapour pressure is of:

Explanation

. The intermolecular forces in n-pentane are weaker than those in isopentane and neopentane. n-pentane has a straight chain, while isopentane and neopentane have branched chains.n-Pentane has a rod-like shape, while neopentane is sphere-like. Rods can touch along their entire length, while the spheres touch only at a point. The more the contact between molecules, the greater the London Dispersian Forces also branched chains make it more difficult for the molecules to interact with each other, and therefore weaken the intermolecular forces.So n-pentane has highest B.P and lowest vapor pressure among these. The weaker intermolecular forces in neo-pentane allow the molecules to escape from the liquid more easily, and therefore have a highest vapour pressure.