Explain the differences in boiling point of a 1-pentene (bp 30°c), 1-bromopentane (bp 129°c) and 1-pentanol (bp 137°c). what intermolecular forces are involved in holding the molecules in the liquid form in each of these as pure substances?

Generally bonds present between molecules are called intermolecular forces. they are three types:
1) Wander Wall forces (London forces)
2) Dipole - dipole interaction.
3) Hydrogen bond.
- As molecular weight increases boiling point also increases due to surface are is directly proportional to Wander Waal forces.
- Dipole-dipole attraction: the attraction between two different polarizable molecules is called dipole- dipole attraction, this attraction play important role in boiling point.
- Hydrogen bond: electrostatic attraction between hydrogen and more electronegative atom is called hydrogen bond.
- The substance which has hydrogen bond have higher boiling point.
1-pentanol has hydrogen bond
1- Bromopentane has dipole - dipole
1-pentene has only London forces
Hydrogen bond > dipole - dipole attraction > London force 

Most smaller stars don't have a radiative zone.