The accepted relative strengths are that hydrogen bonding is greater in strength than dipole-dipole forces that are in turn greater in strength than London dispersion forces (Hydrogen bonding > dipole-dipole forces > London dispersion forces).

Ethanol molecules exhibit London dispersion forces, dipole-dipole forces, and hydrogen bonding between the molecules.

All molecules have London dispersion forces between them.

Molecules with permanent dipoles have dipole-dipole forces: Ethanol has a permanent dipole as it has polar bonds, C–O and O–H, and asymmetric geometry.

Molecules with a hydrogen atom attached to F, O or N possess hydrogen bonding between molecules: Ethanol has an O–H bond, so also has hydrogen bonding between molecules.

Propanal is an aldehyde; aldehyde molecules exhibit London dispersion forces and dipole-dipole forces, but do not have hydrogen bonding between the molecules.

All molecules have London dispersion forces between them.

Molecules with permanent dipoles have dipole-dipole forces: Propanal has a permanent dipole as it has polar bonds, C=O, and asymmetric geometry.

Molecules with a hydrogen atom attached to F, O or N possess hydrogen bonding between molecules: Propanal does not have an O–H bond (the bonds in the functional group are C=O and C–H) so does not have hydrogen bonding between molecules.

Diagram below:

Note that the electrostatic attraction is between a lone pair on the oxygen atom and the δ+ hydrogen atom (not between two hydrogen atoms as in option 3). Thus lone pairs on the oxygen atom are included (option 1), as is the dipole on the O–H bonds (option 2).

The correct answer is 1 and 2 only.

Water is a simple molecule and when truly pure has very poor electrical conductivity.

Water can dissociate into H⁺ and OH^– ions, but they are very few in number and do not provide good conductivity at room temperature.

Water is highly polar, but polar molecules alone cannot conduct electricity, and water does not have delocalised electrons.

It is the ability of water (being so polar) to dissolve ions that results in good electrical conductivity – the dissolved ions in the water can move and carry charge. Thus the correct answer is: Water is highly polar and dissolved ions in the water can move and carry charge.

A high level of volatility (meaning evaporates easily) suggests very weak forces between molecules (only London dispersion forces). Immiscibility with water (not mixing with water; forming two separate layers) suggests that the compound is not polar, and certainly does not have hydrogen bonds.

Thus 'London dispersion forces only' is the correct answer.