To demonstrate that matter is conserved during a physical change, the best procedure would be:
Find the mass of a piece of ice. Let the ice melt. Find the mass of the liquid water.
This experiment shows the conservation of mass because you are not adding or removing matter; you are simply changing the state of the water from solid (ice) to liquid (water). By measuring the mass before and after the melting process, you can confirm that the mass remains constant, thus demonstrating the principle of conservation of matter during a physical change.