Question

10 litres of o2 gas is reacted with 30 litres of co at stp the volume of each gas present at the end reaction

Answer 1

Co + O2 gives 2co2
1 vol. 1 vol. 2 vol up
Co. : Co2
1 vol. : 2 vol
30 L: x
cross multiplying ( assuming vol. of the Co2 to be x)
x = 60 L

Answer 2

Here is the answer. I have used unitary method and limiting reagent calculations