Which set of materials would be best to prepare a wet mount slide of onion skin cells?

Preparing a wet mount slide of onion skin cells requires a few specific materials to ensure the cells are properly observed under a microscope. The correct answer emphasizes the need for a liquid medium to facilitate the viewing of the cells. Water, represented by H2O, serves as the primary reagent that helps to keep the onion cells hydrated and minimizes distortion during microscopy.

When preparing the slide, a drop of water is placed on the slide to create a suitable environment for the cells. This allows for better light transmission and clearer visibility of the cellular structure under magnification. Additionally, water helps to separate the cells, which can prevent overlapping and make it easier to study individual cell characteristics.

The other materials listed, while potentially useful in other contexts, do not directly contribute to the preparation of a wet mount slide. For example, "big and small glass" may refer to various sizes of glassware, but they do not play a role in the immediate task of preparing the slide. A strain could imply staining, which although useful in observing cells more clearly, is not essential for the basic observing of onion skin cells in a wet mount. An eyedropper might assist with applying water, but it is not the primary material needed in this case for creating the wet mount