What should be done with containers that contain magnesium or other metals before reuse?

Rinsing containers that have held magnesium or other metals with nitric acid is important because nitric acid serves to effectively dissolve many metal contaminants and oxidize metallic residues. This ensures that any metal ions that may adhere to the container's surfaces are removed, preventing contamination of future samples.

When containers are used for heavy metals or other reactive substances, residues can interfere with subsequent analyses, leading to inaccurate results. Nitric acid not only cleans but also passivates the surface, reducing the likelihood of residual contamination for future uses.

Other options, while they may seem appropriate, do not ensure the same level of thoroughness in removing metallic residues. For example, rinsing with distilled water might not remove all the metal ions present. Soaking in hydrochloric acid may not be effective against all types of metal residues and could leave some contaminants behind. Leaving the containers as is would clearly not be suitable, as any residual contamination could compromise the integrity of future analyses.