Apublic health research wants to determine the average blood lead concentration for children in elementary school (grades k through 5), but has reason to believe the concentration may differ among neighborhoods where predominantly lower, middle, and upper socio-economic class populations live. select the most appropriate sampling or experimental study design for the above situation.

The most appropriate sampling for this would be "stratified sampling".

Stratified sampling alludes to a kind of testing technique. With stratified sampling, the investigator partitions the populace into discrete gatherings, called strata. At that point, a probability test is drawn from each gathering.  Stratified sampling has a few favorable circumstances over simple random sampling. For instance, utilizing stratified sampling, it might be conceivable to decrease the sample size required to accomplish a given accuracy. Or on the other hand it might be conceivable to increase the accuracy with a similar sample size.