Final answer:
The substance with the least viscosity is ethanol due to its lower molecular weight and hydrogen bonding. Ammonia has the lowest normal freezing point among the given compounds because of its weaker London dispersion forces and the effect on boiling points.
Step-by-step explanation:
Viscosity is a measure of a fluid's resistance to flow.
The substance with the least viscosity among CH3(CH2)4CH3 (hexane), CH3(CH2)3CH3 (pentane), CH3CH2OH (ethanol), and HOCH2CHOHCH2OH (glycerol) is CH3CH2OH (ethanol) due to its lower molecular weight and the presence of hydrogen bonding which tends to reduce viscosity compared to nonpolar compounds with just London dispersion forces.
The compound with the lowest normal freezing point among H2 (hydrogen), CH4 (methane), N2 (nitrogen), and NH3 (ammonia) is NH3 (ammonia).
This is because ammonia has hydrogen bonds, which leads to a higher boiling point and, as a trend, compounds with higher boiling points tend to have higher melting points; hence, when looking at normal freezing points, NH3 with its weaker London dispersion forces compared to the other molecules, has the lowest normal freezing point.