What is the oxidation number for our in nahco3?

I think its -2  in this compound 

Total of the  oxidation numbers must be 0  
so we have 

Na = +1, h = +1 and C = +4

Calculatiing

1 + 1 + 4 + 3(O) =  0

6 + 3O = 0
so O = -6/3 = -2

Answerδh > 0explanationc₆h₆  (s)  → c₆h₆ (l)if you are changing it from a solid to a liquid, you are pretty much melting the solid. this requires heat energy. therefore, the reaction is endothermic (takes in energy); the system enthalpy increases as the reaction proceeds: δh > 0.