A clear sample is still a scientific question — Physical Science: Chemistry

Two bottles contain clear liquids. Visual inspection cannot establish whether either is pure water, a molecular solution or an electrolyte solution. Start with a defined sample boundary and a record of temperature, mass, volume and method. A property comparison becomes evidence only when you know how it was measured and what alternative compositions could produce a similar result.

Suppose three density readings are 1.18, 1.19 and 1.18 g/mL while a relevant reference is 1.00 g/mL. The small spread supports repeatability, but it does not establish accurate identification. Calibration bias, temperature or a genuinely different composition can explain the mismatch. A second independent property can reduce ambiguity, while repeating the same biased method cannot eliminate its common offset.

A separation plan asks which physical property differs. Salt and sand can be separated by selective dissolution, filtration and solvent removal; an ordinary filter cannot split sodium chloride into sodium and chlorine. Keep a species inventory throughout the procedure. Report recovery and purity separately, and preserve results that disagree with your first explanation rather than selecting only convenient trials.