Select the single best answer. Choose the best explanation for the following statement by referring to the compound shown. The compound shown has a diastereomer but no enantiomer. The compound shown has no stereogenic centers, but is a meso compound. The compound shown has no stereogenic centers and is an achiral compound. The compound shown has two stereogenic center and is a chiral compound. The compound shown has two stereogenic centers, but is a meso compound.

The dean of students mailed a survey to a total of 400 students. The sample included 100 students randomly selected from each of the freshman, sophomore, junior, and senior classes on campus last term. What sampling method was used?

Solution: The sampling method used here is stratified sampling. Because the sample included the students from each of the freshman, sophomore, junior and senior classes.

Stratified sampling is is a probability sampling method and a form of random sampling in which the population is divided into two or more groups (strata) according to one or more common attributes and and a sample is selected by some design within each group.