Ammonia's unusually high melting point is the result of: a. dipole-dipole forces.
b. London dispersion forces.
c. hydrogen bonding.
d. covalent bonding.
e. ionic bonding.

c. hydrogen bonding.

Explanation:

Hydrogen bonding occurs when hydrogen is covalently bonded to a highly electronegative atom such as oxygen, flourine, nitrogen etc.

Hydrogen bonds are quite strong and are known to lead to elevated boiling points. As a result of hydrogen bonding, ammonia is known to have a high melting and boiling point compared to its relative molecular mass.

chemical changes occur when a substance combines with another to form a new substance, called chemical synthesis or, alternatively, chemical decomposition into two or more different substances. these processes are called chemical reactions and, in general, are not reversible except by further chemical reactions. some reactions produce heat and are called exothermic reactions and others may require heat to enable the reaction to occur, which are called endothermic reactions. understanding chemical changes is a major part of the science of chemistry.