Butadiene, inhibited, is labeled as a __________.

Correct Answer: Option A — flammable gas

Under 49 CFR 172.101 and international maritime dangerous goods (IMDG) standards, butadiene, inhibited, is classified and labeled as a Division 2.1 flammable gas. The inhibitor is added to prevent dangerous self-polymerization during transport, but the primary hazard remains its extreme flammability in gaseous form.