Which type of scientific statement is defined as a statement of fact that is generally accepted to be true and universal because it has always been observed to be true? theory probability law hypothesis

The answer is law. The laws are scientific explanations considered to be true in any age and any place, under the terms that the law is defined. You can think of two physic laws: The Law of Universal Gravitation and The Law of Conservation of Energy. Theories are also scientific explanations but they are subject to continues proofs, so that they are ratified or substituted with an enhanced or new theory.