Which item would you use to transfer single drops of liquid?

A pipette is an instrument specifically designed for transferring precise volumes of liquid, often down to a single drop. This functionality comes from its narrow opening and graduated scale, which allows for accurate measurement and dispensing based on the volume of liquid inside. Pipettes can be either manual or automatic, and they allow for controlled liquid transfer without spills or contamination.

In contrast, a wash bottle is typically used to dispense larger amounts of liquid for rinsing purposes rather than for precision transfers. A spatula is designed for transferring solid materials or scooping powders, not liquids. Lastly, a test tube is a container used for holding or mixing liquids but is not designed for the specific task of transferring single drops efficiently. Thus, when the goal is to transfer precise single drops of liquid, the pipette is the optimal choice.