Question

heat of combustion of c2h4 is- 337 k.cal .if 5.6 lit o2 is used at a to combustion, heat liberated is?

Answer 1

C2H4 + 3 O2 → 2 CO2 + 2 H2O  

Supposing "lit" to be some weird abbreviation for "liters":  

(5.6 L O2) / (22.414 L/mol) x (1 mol C2H4 / 3 mol O2) x (337 kcal/mol) = 28 kcal