Which of the following is true about melting point determination?
a. At the melting point of a substance, the solid and vapor states exist in equilibrium.
b. An impure compound has a narrow, sharp melting point range.
c. A solid is said to sublime when it first liquefies and then vaporizes to a gas.
d. At the eutectic point, the melting point of a mixture of two compounds is sharp.
e. Although a substance may exist in different crystalline forms, it has only one characteristic melting
point.