in which of the following cases would recrystallization be favored over extraction when purifying a mixture of two solid compounds? i. when a significant difference in pka exists between the two compounds. ii. when there is a significant excess of the desired compound. iii. when the desired compound is freely soluble in the solvent pair at all temperatures. a. i and iii b. ii c. ii and iii d. i and ii e. i, ii, and iii f. none of the above