August 2018 NY Regents Chemistry Exam
25 Which value changes when a Cu atom becomes a Cu^2+ ion? (1) mass number (2) oxidation number
(3) number of protons
(4) number of neutrons
Solution: All free, neutral elements have an oxidation number of zero. Cu atom has an oxidation number of zero while Cu^2+ ion has an oxidation number of 2+
Answer:2
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