in chemistry: The thermodynamically effective concentration of a chemical species or component. In solutions with high ionic strengths, ions interact with each other and are not totally independent chemical units. The interactions affect the boiling point, freezing point, and other properties of the solution. The effective concentration (activity) of an ion in a high ionic strength solution is usually less than the total number of moles in the solution. The activity of an ion is calculated by multiplying its molal concentration by its activity coefficient. In very dilute solutions, activities and molal concentrations are essentially equal.

The term "activity" was found in the following pages:

Unexpected arsenic compounds found in some low rank coals | EVISA's News
Experts in Bioimaging came together in Münster, May 24-25, 2018 | EVISA's News
Instrument database: Beijing Rayleigh Analytical Instrument Corporation (BRAIC) - UV-1201 UV/VIS SPECTROPHOTOMETER
Link database: FDA: Arsenic
Link database: NIPERA: Non-Occupational exposure to Nickel
Link database: Thimerosal - Harmless Vaccine Preservative Or Just Another Toxic Organic Mercury Compound?
Journals database: Journal of Information Science
ISRANALYTICA 2006 | EVISA's Agenda of Events
Instrument database: Knauer GmbH - Fluorescence HPLC Monitor RF-10 AXL
Directory of scientists: John H. Duffus
Link database: EFSA: Scientific Opinion on Arsenic in Food
Link database: Speciation, bioavailability and antigenotoxicity of Selenium species present in Selenium enriched natural products.
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Link database: NIPERA: Pharmacokinetics of Nickel Compounds
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Link database: EFSA: Scientific Opinion on Uranium in Food, in particular mineral water
Link database: Chemical Fact Sheet: Cobalt
Journals database: Animals
Material database: National Research Council of Canada (NRC - CNRC) - NIMS-1: Natural abundance inorganic mercury isotopic certified reference material
Error sources in speciation analysis - Overview | EVISA's News