Question

What evidence of a chemical reaction might you see in bleaching a stain

Answer 1

The properties in the bleach eating away at the stain. The molecules in that destroying the ones causing the stain. As well as it spreads and leaves it's own marks on the clothes, because it destroys the molecules giving the clothing color.

Answer 2

For bleaching a stain, there will be an identifiable odor and it will easily absorb colors and/or stains