What principle states that matter cannot be created or destroyed in a chemical reaction?

The principle that states matter cannot be created or destroyed in a chemical reaction is known as the Law of Conservation of Matter. This law posits that during any chemical reaction, the total mass of the reactants must equal the total mass of the products, meaning that all atoms present in the reactants are accounted for in the products. This fundamental concept is crucial in understanding chemical reactions, as it ensures that mass remains constant throughout the process.

In the context of chemical equations and stoichiometry, this principle enables scientists and students to balance equations accurately, ensuring that the number of each type of atom is the same on both sides of the equation. This understanding is pivotal in performing calculations involving mass and moles in chemistry, thereby providing a foundation for further studies in physical sciences.

Other options, while they relate to scientific principles, do not pertain to the conservation of matter. The Law of Relativity involves descriptions of the interrelation between space and time. The Law of Gravity pertains to the attraction between masses. The Law of Conservation of Energy addresses the transformation of energy, but it does not specifically address the conservation of matter in reactions.