Answer to Question 1
A one-sided alternative is more appropriate since we are not interested in detecting possible low levels of impurity, only high levels of impurity.
Answer to Question 2
Stratified random sampling occurs when the population is divided into strata, and a random sample is drawn from each strata. Cluster sampling occurs when the population is divided geographically into clusters, and a census is performed on each chosen cluster. A researcher would typically choose one of these methods to ensure the representation of subsamples that may constitute small proportions of the sample.