2C2H2(l) +5O2(g)→ 4Co2(g) + 2H2O
The limiting reactant for reaction above is O2
explanation
The limiting reagent is determined using mole ratio of both reactant.
that is the mole ratio of C2H2:O2 which is 2:5 .
The mole ratio above implies that 37.0 mole of C2H2 needs 37.0 moles x5/2=92 moles of O2.
Since the available moles of O2 was 81.0 mole and 92 moles are required to completely react with C2H2 , O2 is the limiting reagent.