Which of the following is an example of an analytical result in concentration?

The correct choice represents an analytical result in concentration because it provides a quantitative measure of the amount of lead present in a specified mass of material. Specifically, mg/kg indicates the number of milligrams of lead per kilogram of the sample, which is a common unit used in various analytical assessments, including those involving soil, dust, and other materials that may contain lead.

This unit of measure allows assessors to effectively gauge the contamination level in the sample by relating the amount of lead directly to the weight of the material being analyzed. This concentration metric is essential for evaluating risks associated with lead exposure and for further regulatory or safety compliance.

Other options present different contexts: while mg/cm² and µg/ft² refer to concentration specifically in terms of area sampling, these are less common in the context of lead risk assessment compared to mg/kg. The unit µg/dL is typically used in clinical settings to measure concentrations in blood and does not apply to non-biological samples typically examined in lead risk assessments.