The law of conservation of mass states that mass cannot be created or destroyed in a chemical reaction. It can only be rearranged or transformed into different forms.

Option 1: When 12 gm of carbon is heated in vacuum, there is no change in mass. This example follows the law of conservation of mass because the mass of carbon remains the same before and after heating. The carbon atoms simply rearrange themselves to form different compounds, but the total mass of carbon remains constant.

Option 2: Weight of platinum wire is the same before and after heating. This example also follows the law of conservation of mass because the mass of the platinum wire remains unchanged even after heating.

Option 3: A sample of air increases in volume when heated at constant pressure but mass remains unchanged. This example does not illustrate the law of conservation of mass. While the mass of the air sample remains constant, the volume increases, indicating a change in the state or physical properties of the substance.

Option 4: 12 gm of carbon combines with 32 gm of oxygen to give 44 gm of carbon dioxide. This example best represents the law of conservation of mass. The total mass of the reactants (carbon and oxygen) is equal to the total mass of the product (carbon dioxide