If a question gives equal total reactants and total products which law is likely?

Correct answer: Conservation of mass

The direct answer is A, conservation of mass. This law states that in a chemical reaction matter is not created or destroyed. At the level of a closed reaction, the total mass of all reactants equals the total mass of all products. The reasoning is simple: reactants are the substances present before the reaction, and products are the substances formed after it. If the question specifically compares their total amounts or masses and says they are equal, it is pointing to conservation of mass. Option A is correct because equality of total reactant and product mass is its central idea. Option B, definite proportions, deals with the fixed ratio of elements inside one pure compound, not with total reactant and product mass. Option C, multiple proportions, compares different compounds made by the same two elements, where masses combine in small whole-number ratios. Option D, gaseous volumes, concerns volume relations of reacting gases at the same temperature and pressure. Do not confuse equal mass with equal composition. Exam cue: words such as total mass, before reaction, after reaction, neither created nor destroyed, and reactants equal products usually indicate conservation of mass.