How is substance composition measured and reported?

The composition of a substance is measured to know what it is made of and in what proportion. Scientists use percent composition to describe how much of each element is present in a compound. For example, in water (H₂O), hydrogen makes up about 11.2% and oxygen about 88.8% by mass.

Methods such as chemical analysis, spectroscopy, and chromatography are used to measure composition accurately. In mixtures, composition can also be expressed as mass percent, mole fraction, or volume percent depending on the type of mixture.

The results are reported in scientific units such as grams, moles, or percentages, allowing chemists to write formulas and predict reactions correctly. Measuring composition is essential for identifying substances, ensuring product quality in industries, and understanding chemical reactions.