Final answer:
The correct wording for a confidence interval estimate of the population mean is option C: One can conclude with 95% confidence that the average concentration level is between 4.2 mg/kg and 5.6 mg/kg.
Step-by-step explanation:
The correct wording for a confidence interval estimate of the population mean is option C: One can conclude with 95% confidence that the average concentration level is between 4.2 mg/kg and 5.6 mg/kg.
This statement accurately reflects the concept of a confidence interval, which represents a range of values within which the true population mean is estimated to lie with a specified level of confidence.