Answer:
D. decomposing
General Formulas and Concepts:
Chemistry
Explanation:
A would be incorrect because mixing 2 things together doesn't necessarily create a chemical change. Take oil and water for example. You can mix the 2 and it would not have a chemical change.
B would be incorrect because you are simplify changing the state of matter of the object. Iron in solid form is still iron in liquid form; there is no chemical change.
C would be incorrect for similar reasons as B. You are simply changing the state of matter.
D would be the remaining and correct answer. Decomposing changes one object into a different one by chemically changing.