Ang arseniko o arsenik (Kastila: arsenico, Ingles: arsenic) ay isang uri ng elementong kimikal at lasongmetaliko. Mayroon itong atomikong bilang na 33, atomikong timbang na 74.992, balensiyang 3 o 5, at sagisag na As. Natutunaw ang abuhing arseniko sa temperaturang 817 °C (habang nasa 28 na presyong atmosperiko, sagisag atm), sumisingaw (sublima) sa temperaturang 613 °C, at may espesipikong grabidad na 5.73. Mayroon itong tatlong anyong alotropiko, na nasa anyong may kulay na dilaw, itim, at abuhing kristalina. Ginagamit ang arseniko bilang insektisidyo o pamatay ng pesteng mga kulisap, pamatay ng mapinsalang mga damo, at inihahalo rin sa mga aloy.[11]
↑ 3.03.1Arblaster, John W. (2018). Selected Values of the Crystallographic Properties of Elements. Materials Park, Ohio: ASM International. ISBN978-1-62708-155-9.{{cite book}}: CS1 maint: date auto-translated (link)
↑Gokcen, N. A (1989). "The As (arsenic) system". Bull. Alloy Phase Diagrams. 10: 11–22. doi:10.1007/BF02882166.{{cite journal}}: CS1 maint: date auto-translated (link)
↑Abraham, Mariham Y.; Wang, Yuzhong; Xie, Yaoming; Wei, Pingrong; Shaefer III, Henry F.; Schleyer, P. von R.; Robinson, Gregory H. (2010). "Carbene Stabilization of Diarsenic: From Hypervalency to Allotropy". Chemistry: A European Journal (sa wikang Ingles). 16 (2): 432–5. doi:10.1002/chem.200902840. PMID19937872.{{cite journal}}: CS1 maint: date auto-translated (link)
↑Ellis, Bobby D.; MacDonald, Charles L. B. (2004). "Stabilized Arsenic(I) Iodide: A Ready Source of Arsenic Iodide Fragments and a Useful Reagent for the Generation of Clusters". Inorganic Chemistry (sa wikang Ingles). 43 (19): 5981–6. doi:10.1021/ic049281s. PMID15360247.{{cite journal}}: CS1 maint: date auto-translated (link)
↑Weast, Robert (1984). CRC, Handbook of Chemistry and Physics. Boca Raton, Florida: Chemical Rubber Company Publishing. pp. E110. ISBN0-8493-0464-4.{{cite book}}: CS1 maint: date auto-translated (link)