0.210 mol of octane is allowed to react with 0.760 mol of oxygen. which is the limiting reactant?

 0.69 mol / 25 eq = 27.6 mmol O2 
0.20 mol / 2 eq = 100 mmol octane 

therefore... 

a) oxygen is the limiting reagent 
b) 27.6 mmol x 18 eq = 497 mmol or 0.0497 moles H2O produced. 
c) 27.6 mmol x 2 eq = 55.2 mmoles octane consumed 
200 mmol - 55.2 mmol = 144.8 mmol or 0.145 moles octane remaining. 

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