Question

A student records the mass of a piece of iron. The iron is then left outside until it rusts. What type of reaction occurs, and how does the mass of the object after rusting compare with its original mass?

Answer 1

the mass is the same but the reaction is called decay. 

Answer 2

Decomposition; The mass of the iron is grater

Step-by-step explanation:

The Iron combines with Oxygen to form Rust ( Iron Oxide) This is an Oxidation reaction. It is also an Oxidation Reduction reaction. The Iron Oxide has more mass than the original Iron.