Answer: 1.38 L O2
Step-by-step explanation:
2CO + O2 = 2CO2
So, 
1 mole CO = 22.4 L CO
2 mole CO = (22.4 ×2)L CO 
 = 44.8 L CO 
And 1 mole O2 = 22.4 L O2
44.8LCO are burned by 22.4LO2 1 L CO are burned by 22.4÷ 44.8
 = 0.5 L O2
2.76L CO are burned by0.5×2.76
 = 1.38 L O2 
So, 1.38 L O2 are needed to burn 
2.76 L CO