A student says conservation of mass means each product mass equals each reactant mass. What is the mistake?

Correct answer: Total mass is equal not each substance

The direct answer is option A: total mass is equal, not the mass of each individual substance. Conservation of mass means that in a closed chemical reaction, the sum of the masses of all reactants equals the sum of the masses of all products. It does not mean that every product has the same mass as every reactant. For example, several reactants may combine to make one product, so the product mass can equal their combined mass while differing from each separate reactant mass. Option A correctly identifies the student's mistake: the word total is essential. Option B, no mass is equal, is wrong because total mass is conserved. Option C says only colour is equal; colour is not what the law conserves. Option D says gases should be removed, but removing a gas can make a system appear to lose mass and would violate the closed-system condition. Thus the student confused individual masses with the sum of all masses. Exam cue: conservation means total before equals total after, not each item before equals each item after.