Answer:
" An observational study was conducted and the response variable is the concentration of the chemical"
Explanation:
" An observational study was conducted and the response variable is the concentration of the chemical"
Here,
the observations are being taken i.e the measurements are made about the concentration of a certain chemical.
In observational study, the observer measures or observes the response without altering or intervention with the source.
Response variable is the quantity or response which is to be observed to know its impact or to explain the measured quantity.