Answer:
Chemical change
Step-by-step explanation:
If you start with substance A and B and you produce C, you have witnessed a chemical change and this is a synthesis or combination reaction.
A + B → C
We know this because from the two different reactants, a new substance C has been formed.
The substance C is produced via a chemical change.
In a chemical change, new kinds of products are usually formed and the reaction is not easily reversible.