The amount of oxygen required for the complete combustion of 1 mole of Acetylene is?

${\text{2 C}}_{\text{2}}{\text{H}}_{\text{2}}{\text{+5 O}}_{\text{2}}\stackrel{ }{\to }{\text{4 CO}}_{\text{2}}{\text{+2 H}}_{\text{2}}\text{O}$

For the combustion of 2 mole of Acetylene 5 mole of oxygen required. For the combustion of 1 mole of Acetylene 2.5 moles of oxygen required.  Molecular weight is 32. 

          2.5 moles of oxygen weight is 2.5*32=80g