In each pair of compounds, pick the one with the higher vapor pressure at a given temperature. Explain your reasoning. a. Br₂ or I₂ b. H₂S or H₂O c. NH₃ or PH₃

Verified step by step guidance

1. Step 1: Understand that vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid or solid phase. It is influenced by intermolecular forces; weaker forces result in higher vapor pressure.
2. Step 2: For part (a), compare Br_2 and I_2. Both are halogens and nonpolar molecules, but Br_2 has weaker London dispersion forces than I_2 due to its smaller size and lower molar mass, leading to higher vapor pressure.
3. Step 3: For part (b), compare H_2S and H_2O. H_2O has strong hydrogen bonding due to its highly polar O-H bonds, while H_2S has weaker dipole-dipole interactions. Therefore, H_2S has a higher vapor pressure.
4. Step 4: For part (c), compare NH_3 and PH_3. NH_3 can form hydrogen bonds due to the presence of N-H bonds, whereas PH_3 cannot form hydrogen bonds and has weaker van der Waals forces, resulting in higher vapor pressure for PH_3.
5. Step 5: Summarize that the compound with weaker intermolecular forces in each pair will have the higher vapor pressure at a given temperature.