What tool is best suited for mixing liquids or chemicals in a container?

A stirring rod is specifically designed for the purpose of mixing liquids or chemicals in a container effectively. Its long, slender shape allows for easy insertion into various sizes of containers without the risk of spilling the contents. The smooth surface of the rod ensures that it does not react with the substances being mixed, maintaining the integrity of the solutions. This makes it an ideal tool for ensuring that components are thoroughly combined, whether in a laboratory setting or during experiments in biology or chemistry.

In contrast, a test tube holder is intended for safely holding and manipulating test tubes, particularly when they are hot or contain hazardous materials. A test tube brush serves the purpose of cleaning test tubes and other glassware, ensuring proper hygiene and preparation for subsequent use. A ruler is primarily a measurement tool, which does not have any relevance in mixing liquids or chemicals.