This flask originally held some copper wire and a clear solution of nitric acid. the two substances reacted and produced a brown gas and a blue solution. this reaction cannot be reversed. evidence of a chemical reaction is shown by

the formation of a gas.

Explanation:

A chemical reaction is a transformation or chemical phenomenon that occurs when the nature or composition of matter is changed. In this case, the initial particles (which can be molecules, atoms, ionic agglomerates, ions, etc.) are as if disassembled and their atoms rearrange themselves, assembling new molecules, agglomerates, atoms, ions, etc., that is, new substances. In short, a chemical reaction generates a new substance that was not initially in that environment.

For this reason, in the case of the question shown above, the evidence that a chemical reaction has occurred is the production of a gas. Gas is the substance created by this reaction.

to improve her experimental investigation, dalila should add a row in which no fertilizer is used. by a having a contrasting row in which no fertilizer is used, she will have a control group that will her understand the effects of the fertilizer in the plant developments vs the development of the plant when no fertilizer is used.