Which equation is used to calculate mg/cm2 for a paint chip sample?

The chosen response is correct because it provides the appropriate formula for calculating the concentration of lead in milligrams per square centimeter (mg/cm²) for a paint chip sample. This calculation is essential in lead risk assessment to determine the amount of lead present in a specific area of a paint sample, which is crucial for evaluating potential exposure risks.

The formula incorporates the weight of lead derived from the sample in milligrams and adjusts for the total mass of the sample through the subsampling technique, allowing for an accurate representation of lead concentration over a defined area. Specifically, multiplying the weight of lead from the sample by the ratio of the total sample weight to the subsample weight helps to account for any dilution or concentration effects that might occur during sampling, ensuring precision in the results. The final division by the area in square centimeters normalizes the concentration, yielding the desired units of mg/cm².

This method is especially useful in lead risk assessment as it conveys how much lead is present in a paint layer over a specific surface area, informing remediation strategies and health risk evaluations.