Which substance will have the highest boiling point?

To determine which substance will have the highest boiling point, we need to consider the intermolecular forces present in each substance. The strength of the intermolecular forces will determine the boiling point, as substances with stronger intermolecular forces require more energy to break those forces and transition from a liquid to a gas.

Let's analyze each substance and its intermolecular forces:

A) He (Helium)
- Helium is a noble gas and exists as individual atoms.
- It exhibits weak London dispersion forces due to its temporary shift in electron density.
- Helium has the lowest boiling point among the given substances.

B) CsF (Cesium Fluoride)
- Cesium fluoride is an ionic compound composed of Cs+ and F- ions.
- Ionic compounds have strong electrostatic forces of attraction between oppositely charged ions.
- The ionic bond in CsF is stronger than the intermolecular forces in the other substances.
- CsF has a high boiling point compared to the other substances.

C) NH3 (Ammonia)
- Ammonia is a polar molecule with a central nitrogen atom bonded to three hydrogen atoms.
- It exhibits dipole-dipole interactions between the positive hydrogen end and the negative nitrogen end.
- Ammonia also experiences hydrogen bonding, which is a strong intermolecular force due to the presence of hydrogen bonded to a highly electronegative atom (nitrogen).
- Despite hydrogen bonding, ammonia has a lower boiling point compared to CsF.

D) CHCl3 (Chloroform)
- Chloroform is a polar molecule with a central carbon atom bonded to three hydrogen atoms and one chlorine atom.
- It exhibits dipole-dipole interactions between the positive hydrogen end and the negative chlorine end.
- Chloroform does not experience hydrogen bonding because it lacks a hydrogen atom bonded to a highly electronegative atom.
- Although chloroform has dipole-dipole interactions, its boiling point is lower than that of CsF.

In summary, CsF will have the highest boiling point among the given substances. This is due to the strong ionic bond present in CsF, which requires a significant amount of energy to break and transition from a liquid to a gas.

CsF is the most ionic compound
option b