Which scientific tool is the most useful when trying to convert a known amount of grams of water to moles of water?
a scale
a thermometer
a periodic table
a spectrophotometer

The correct answer is the third option. A periodic table is the scientific tool that is most useful when trying to convert a known amount of grams of water to moles of water. Converting the amount of a substance from grams into moles, the molar mass is needed where it is the mass of a substance per 1 mole of the substance. This value is written in the periodic table.