The correct procedure to demonstrate that matter is conserved during a chemical change or reaction is:
Find the mass of an acid and a base. Combine them to produce water and a salt. Find the mass of the water and salt.
This procedure illustrates the law of conservation of mass, which states that in a closed system during a chemical reaction, the total mass of the reactants (acid and base) will equal the total mass of the products (water and salt). The other methods, while they demonstrate aspects of physical changes (melting, tearing) or incomplete aspects of chemical changes (burning), do not fully capture the conservation of mass in the way that a chemical reaction does.