Final answer:
The substances HCOOH, H2S, and Ar, when listed in order of increasing intermolecular forces, are as follows: Ar, H2S, then HCOOH, with HCOOH having the strongest due to hydrogen bonding.
Step-by-step explanation:
To list the substances HCOOH, H2S, and Ar in order of increasing intermolecular forces, we need to consider the types of intermolecular forces each substance can exhibit.
- Argon (Ar) is a noble gas and thus only exhibits dispersion forces, which are the weakest type of intermolecular force.
- Hydrogen sulfide (H2S) is a polar molecule with dipole-dipole interactions in addition to dispersion forces. H2S, however, does not hydrogen bond because sulfur is not one of the three elements that commonly participate in hydrogen bonding (nitrogen, oxygen, and fluorine).
- Formic acid (HCOOH) can exhibit hydrogen bonding due to the presence of the hydrogen-oxygen bond, along with dipole-dipole interactions and dispersion forces. Hydrogen bonding is generally the strongest type of intermolecular force present in this list.
Therefore, the correct order from weakest to strongest intermolecular forces is: Ar < H2S < HCOOH.