1. In chemistry, the Avogadro constant, commonly denoted NA, is a conversion constant or ratio between an amount of substance and the number of particles that it contains. The particles in question are any designated elementary entity, such as molecules, atoms, ions, or ion pairs. It is an SI defining constant with the exact value 6.02214076×1023 mol−1 (reciprocal mole). The numerical value of this constant when expressed in terms of the mole is known as the Avogadro number, commonly denoted N0. The Avogadro number is an exact number equal to the number of constituent particles in one mole of any substance (by definition of the mole), historically derived from the experimental determination of the number of atoms in 12 grams of carbon-12 (12C) before the 2019 revision of the SI, i.e. the gram-to-dalton ratio, g/Da. Both the constant and the number are named after the Italian physicist and chemist Amedeo Avogadro. The Avogadro constant is used as a proportionality factor to define the amount... from wikipedia.org NA, N.A., Na, nA or n/a may refer to: == Chemistry and physics == Sodium, symbol Na, a chemical element Avogadro constant (NA) Nucleophilic addition, a type of reaction in organic chemistry Numerical aperture, a number that characterizes a range of angles in an optical system nA, the symbol for nanoampere Naturally aspirated engine == Biology and medicine == Na (tree) or Mesua ferrea, a species of tree native to Sri Lanka Neuroacanthocytosis, a neurological condition Nomina Anatomica, a former international standard for human anatomical nomenclature Noradrenaline, a hormone Nucleic acid analogue, compounds analogous to naturally occurring RNA and DNA == Places == === Current === Namibia (ISO country code) Naples (car number plate code: NA), Italy North America, a continent North Africa, a subcontinent === Historical === Netherlands Antilles (former international vehicle registration code: NA) Na (Chinese state), a small state of the Chinese Zhou dynasty from the 11th to 8th centuries BC Nakoku... from wikipedia.org