The magnitude of the charge on an ion, given in arabic numerals followed by the sign of the charge, in parentheses without a space, immediately after the name of an ion, e.g. iron(2+), hexacyanoferrate(4−).
Note:
The term @E02231@ is no longer recommended.
Source:
Red Book, 3rd ed., p. 66 (https://doi.org/10.1515/pac-2014-0718)