Which piece of lab glassware is most accurate for measuring 100 mL of water?

The most accurate piece of lab glassware for measuring 100 mL of water is the volumetric flask. Volumetric flasks are specifically designed for precise measurements of liquid volumes. They have a narrow neck with a calibration mark that indicates a specific volume, ensuring that the liquid is measured to that exact capacity when filled to the mark. This characteristic makes the volumetric flask ideal for preparing solutions of known concentrations, where accuracy is crucial.

The graduated cylinder, while also used for measuring liquids, has a wider neck and is generally less precise than a volumetric flask. Its scales are designed for general use and may introduce more error in measurement compared to the tightly defined volume of a volumetric flask.

A beaker offers a rough estimate of volume but is not designed for precision measurement, as its markings can be quite broad and not finely calibrated. Similarly, a pipette is used for transferring specific volumes of liquid rather than measuring them in larger quantities; it is precisely calibrated for specific measurements but typically does not accommodate a volume as large as 100 mL.

Therefore, for accurate measurement of 100 mL of water, the volumetric flask stands out as the most reliable choice.