# Chapter 3 Chemical Reactions - 3-9 Classifying Reactions in Aqueous Solution - Applying Chemical Principles - Questions - Page 135: 3

Two 2+ and one 3+.

#### Work Step by Step

Oxidation numbers: O: -2, Y: +3, Ba: +2 For copper (one is +2): $0= +3+2\times2+2+nOx_{Cu}\times2-2\times7$ $nOx_{Cu}=+5/3\rightarrow wrong$ For copper (two are +2): $0= +3+2\times2+2\times2+nOx_{Cu}-2\times7$ $nOx_{Cu}=+3$

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