What is an example of a negative control in an experiment?

An example of a negative control occurs during clinical trials. A placebo is an inert treatment given to participants in the control group to mimic the experimental treatment without having any therapeutic effect. This helps researchers assess the true efficacy of the experimental treatment by comparing it to the placebo response. 

Another example is during an experiment evaluating the impact of a new fertilizer on plant growth, the negative control group consists of plants grown without the fertilizer, but subjected to identical conditions as the experimental group.