What is defined as the law that specifies the rights and duties of individuals and collective bodies?

Substantive law is the correct choice because it encompasses the set of laws that delineate the rights and responsibilities of individuals and collective bodies within a legal system. These laws define what constitutes legal rights and obligations, including areas such as personal injury, contract law, and property law.

Substantive law provides the foundational framework for legal practice by addressing the substance of legal issues rather than merely the procedures required to resolve them. It is critically important for individuals to understand their rights and duties under the law, as this knowledge empowers them to navigate legal situations effectively.

In contrast, procedural law refers to the processes and rules that govern how the legal system operates, detailing how legal cases are handled and how rights are enforced. Conflict of laws, on the other hand, deals with which jurisdiction's laws are applicable in a legal dispute that spans multiple jurisdictions. Executive power refers to the authority held by the executive branch of government to enforce laws, which does not define individual rights and duties directly. Thus, substantive law is distinctly focused on defining those rights and duties, making it the most appropriate answer to the question.