Dear Student,
CH4 + 2O2 → CO2 +2H2O
multyplying it by 2 because 2 mole of methane will be used for combustion
2CH4 + 4O2 → 2CO2 +4H2O2
number of mole of CO2 produced in combustion = 2
As 1 mole contains 6.08 1023 molecule so 2 mole will contain
so number of molecule produced after combustion is 12.16 1023
Regards