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.