Identify the area of the nfpa 704 marking that indicates the reactivity hazard?

NFPA 704 Hazmat color codes:

blue -- health hazard (4 being deadly)

red -- fire hazard (4 being flash point below 73 F)

yellow -- reactivity (4 may detonate) and

white -- specific hazard (no water, radioactive, acid, alkali, corrosive, oxidizer)