- Iron is a kind of metal
- Nails are often made of iron
- Therefore, nails are made of metal

- Nails are made of metal
- Metals in contact with water and oxygen will rust
- Hence, nails in contact with water and oxygen will rust

- Nails in contact with water and oxygen will rust
- Rust forming is a kind of chemical change
- So, nails rusting in water is a kind of chemical change

Therefore, nails rusting in water is a kind of chemical change
Q: Which is an example of a chemical change?
Context:
- Iron is a kind of metal 
- Rust forming is a kind of chemical change 
- Nails are often made of iron 
- Metals in contact with water and oxygen will rust