Which of the following has been adopted by all US states as law?

The correct choice is NFPA 70, also known as the National Electrical Code (NEC). It has been widely adopted by all US states as part of their building and electrical codes. This code establishes the minimum standards for electrical installations to ensure safety from electrical hazards. Given its critical importance in preventing electrical fires and ensuring safe electrical practices, states have integrated the NEC into their regulations to promote consistency and safety across various jurisdictions.

By contrast, while NFPA 40 (which pertains to the storage and handling of explosive materials), NFPA 101 (the Life Safety Code, addressing building egress and safety for occupants), and NFPA 25 (which covers the inspection, testing, and maintenance of water-based fire protection systems) are significant and widely referenced, they have not reached the same level of universal adoption as NFPA 70. Each of these codes serves specialized functions and may be adopted to varying degrees by different states based on local needs and regulations.