the high temperature generated by the burning of acetylene c2h2 finds application in the acetylene torch used for cutting and welding?

Molar mass of O₂ = 16.00 × 2 g/mol = 32.00 g/mol

2C₂H₂ + 5O₂ → 4CO₂ + 2H₂O
Mole ratio C₂H₂ : O₂ = 2 : 5

No. of moles of C₂H₂ combusted = 1.20 mol
No. of moles of O₂ required = (1.20 mol) × (5/2) = 3.00 mol
Mass of O₂ required = (3.00 mol) × (32.00 g/mol) = 96.0 mol

Just a point here and a criticism of the question. The oxyacetylene torch uses gaseous oxygen not liquid oxygen although the inclusion of the word liquid" is pointless. As the person who set you the question should have known, oxygen is a so called "permanent gas" and cannot be liquified by pressure alone above -119 deg C. The O2 in cylinders is a supercritical fluid not a liquid.