I believe it’s Refractive index
The element used in advertising signs is neon.
Answer : During chemical changes only.
Explanation : A chemical change is usually when a compound or molecule undergoes a change which is normally irreversible and it generates a new product than it was before.
So, when we consider the process of making up of substances from atoms it makes the substance as an irreversible product.
Also a new product which is formed is the substance which is not at all similar to atoms.
