Determine the oxidation number for the indicated element in each of the following compounds: (a) Co in LiCoO2, (b) Al in NaAlH4, (c) C in CH3OH (methanol), (d) N in GaN, (e) Cl in HClO2, (f) Cr in BaCrO4.

Answer 1

LiCoO2.
Li is +1.
O is -2; there are two of them for a total of -4. To make the compound zero (all compounds are zero) Co must be +3.
NaAlH4.
Na is +1. Al is +3. That makes H a total of -4 or -1 for each H. (H is a hydride in this compound)
The others are done the same way.

Answer 2

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