What Unit is Isotopic Fractionation Reported As

Question

What unit is isotopic fractionation reported as?
A) parts per billion
B) parts per hundred
C) parts per thousand
D) parts per trillion

Accepted Answer

Isotopic fractionation is commonly reported in units of parts per thousand (‰). This represents the ratio between the isotopes of interest (e.g. 13C/12C or 18O/16O) in a sample relative to a standard reference material, expressed as a deviation in parts per thousand from the standard. Other units like parts per billion, parts per hundred, and parts per trillion are less commonly used for this purpose.