Answer:
The correct answer is (4) a ratio variable
Explanation:
Nominal, ordinal, interval, or ratio data are the four fundamental levels of measurement scales that are used to capture data.
Nominal scales are used for labeling variables, without any quantitative value.
Ordinal the order of the values is what is significant, but the differences between each one is not really known.
Interval we know both, the order and the exact differences between the values
Ratio they have the order, the exact value between units, and have an absolute zero
In this case, the concentration of DDT (C14H9Cl5), in milligrams per liter is a RATIO, because it has order, the exact value between units, and have an absolute zero