You are on a containership carrying a tank container that had been filled with sodium hydroxide solution. The container is empty but has not been cleaned. Which, if any, placard is required?

Correct Answer: Option B — Black and white corrosive placard

Under 49 CFR hazardous materials regulations, empty uncleaned packagings and portable tanks retain residue hazards and must continue to display the appropriate hazard placards, such as the corrosive placard, corresponding to the previous contents.