(a) Explain why ammonia has a low boiling point

Explanation: Ammonia has pretty strong intermolecular forces because it can form hydrogen bonds, however it can't form as many hydrogen bonds per molecule as water and so its boiling point and melting point are lower.

c- cold periods in earth's history during which glaciers covered much of the surface.

explanation:

a. energy is absorbed in the reaction.

if in a given reaction the energy of products is greater than the energy of reactants it means that reaction is endothermic and during the reaction, the energy is absorbed by reactants. in an endothermic reaction, the products have more stored chemical energy than the reactants. and in this reaction the reactants are more stable than products before the compounds with less energy are always more stable.