Amount of substance
= Amount of substance
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Amount of substance measures a count of specified entities, such as <chemical atoms>, <molecules>, <ions>, or <Electrons>, using the <mole> as its <SI> base unit. It differs from <mass>: equal amounts of substance of different <chemical substances> contain equal entity counts but generally have different <masses>. If $N$ entities are present, $n=N/N_{\mathrm A}$, where $N_{\mathrm A}$ is the <Avogadro constant>. The specified entity matters: one <mole> of <water> <molecules> contains two <moles> of <hydrogen> <chemical atoms>. https://www.bipm.org/en/si-base-units/mole[BIPM, definition of amount of substance and the mole]{ref}