The observed mass increase when steel wool burns demonstrates that oxygen from the air is incorporated into the product. Which statement best describes this phenomenon?

• A. Mass is created from nothing.
• B. Oxygen from the air becomes part of the product, increasing total mass.
• C. No reaction occurs.
• D. The mass decreased.

Answer: (B)

When something burns in air, it reacts with oxygen from the surroundings to form a new compound. The observed mass increase happens because oxygen from the air becomes part of the product, so the product’s mass equals the original iron plus the mass of the absorbed oxygen. This shows that the air contributes material to the reaction; mass isn’t created from nothing, a reaction does occur, and the total mass increases because it includes the gained oxygen.