choose the substance with the lowest boiling point.\no h₂o₂\no cf₂h₂\no nbr₃\no f₂\no h₂s\nquestion 13 1…

Explanation:

Step1: Analyze intermolecular forces

Boiling - point is related to intermolecular forces. Stronger intermolecular forces lead to higher boiling - points. The main types of intermolecular forces are hydrogen - bonding, dipole - dipole forces, and London dispersion forces.

Step2: Evaluate each substance in the first question

• $\mathrm{H_2O_2}$ has hydrogen - bonding due to the presence of $O - H$ bonds, which results in relatively high boiling - point.
• $\mathrm{CF_2H_2}$ is a polar molecule, so it has dipole - dipole forces.
• $\mathrm{NBr_3}$ is a polar molecule with dipole - dipole forces.
• $\mathrm{F_2}$ is a non - polar molecule. It only has London dispersion forces. Since London dispersion forces are the weakest among the mentioned intermolecular forces for small molecules, $\mathrm{F_2}$ has a low boiling - point.
• $\mathrm{H_2S}$ is a polar molecule with dipole - dipole forces.

Step3: Evaluate each substance in the second question

The given molecules are alkanes. For alkanes, boiling - point increases with increasing molecular weight (number of carbon atoms) and decreases with branching. The first two molecules have 5 carbon atoms and the third has 4 carbon atoms. Among the 5 - carbon alkanes, the straight - chain alkane has a higher boiling - point than the branched - chain alkane due to more surface area contact and stronger London dispersion forces.

Answer:

First question: $\mathrm{F_2}$ Second question: The straight - chain alkane with 5 carbon atoms (the second structure in the second question)