Question

how can we tell this banana ripening is a chemical change?
formation of a solid has occurred.
bubbles have formed.
a new color has appeared.

Explanation:

Chemical changes often involve the formation of new substances. In the case of banana ripening, a new color (e.g., from green to yellow) indicates a chemical change as it is due to the formation of new pigments (such as carotenoids) which are new substances. Formation of a solid (not relevant here as bananas don't form a solid in ripening in the context of this question) and bubble formation (not a typical sign in banana ripening) are not the key indicators.

Answer:

A new color has appeared.