- Iron in contact with water and oxygen will rust
- Rust forming is a kind of chemical change
- So, iron in contact with water and oxygen causes a chemical change

- Iron in contact with water and oxygen causes a chemical change
- Chemical reactions cause chemical change
- So, iron in contact with water and oxygen is an example of chemical reactions

Hence, iron in contact with water and oxygen is an example of chemical reactions
[Question]Which is an example of substances reacting chemically?
[Context]- Chemical reactions cause chemical change 
- Iron in contact with water and oxygen will rust 
- Rust forming is a kind of chemical change