Árgọ̀nù je elimenti kemika kan to ni ami-idamo Ar ati nomba atomu 18. O wa ninu egbe 18 (awon efuufu abiire) lori tabili idasiko awon elimenti. Argonu ni efuufu keta to wopo julo ninu afefeayika Aye, ni 0.93% (9,300 ppm), eyi so di eyi to repete ni ona bi 23.8 bi ti efuufu inu afefeayika tto wopo julo to tele, eyun dioksidi karbonu (390 ppm), ati to po repete ni ona to to 500 bi ti efuufu abiire keji to wopo, eyun neonu (18 ppm). Bi gbogbo argonu yi lo je argonu-40 radiogeniki to wa lati ituka potassium-40 ninu igbele Aye. Ni agbalaaye, argonu-36 ni isotopu argonu to wopo julo, nitoripe o je isotopu argonu to je dida pelu stellar ikojonukleu irawo ninu awon supanofa (awon irawo akomonamona). "IUPAC Periodic Table of the Elements and Isotopes". King's Center for Visualization in Science. IUPAC, King's Center for Visualization in Science. Retrieved 8 October 2019.  Magnetic susceptibility of the elements and inorganic compounds, in Handbook of Chemistry and Physics 81st edition, CRC press.