In which of the following years did Antoine Lavoisier discover the law of conservation of mass and state that mass is conserved in a chemical reaction?

The correct option is 1789.

Step-by-Step Explanation:

1. Understanding the Law of Conservation of Mass:
The law of conservation of mass states that matter (or mass) can neither be created nor destroyed in a chemical reaction. In other words, the total mass of the reactants before a chemical reaction must be exactly equal to the total mass of the products formed after the reaction.

2. Historical Context:
French chemist Antoine Lavoisier performed careful quantitative measurements of chemical reactions, such as the combustion of phosphorus and sulfur, and the oxidation of metals. He demonstrated that even though substances change their state or appearance, their total mass remains constant.

3. Year of Publication:
Antoine Lavoisier formulated and widely published this fundamental law of chemistry in his landmark textbook, Traité Élémentaire de Chimie (Elementary Treatise on Chemistry), which was published in the year 1789. This work laid the foundation for modern quantitative chemistry.