Answer:
This is a description of a chemical change.
Explanation:
A chemical change will change the identity of the original material, which creates a new, different material.
An example of this is burning wood. Burnt wood turns into ash, which has a vastly different outward appearance, and the fire changes the molecular structure, which makes the product a completely different material.
The original substances were soft and silvery, and yellow and gaseous. The resulting substance is a white crystal, which has totally different properties.
The change created a different substance with different properties from the original substances, showing that a chemical change occurred.
This example describes sodium and carbon reacting to form NaCl, commonly known as table salt. Na is a silvery white material that reacts violently with water, and Cl is a toxic gas. They form a safe, stable compound that is edible and delicious.