What mass of natural gas (ch4) must you burn to emit 269 kj of heat? ch4(g)+2o2(g)âco2(g)+2h2o(g)î´hârxn =â802.3kj express the mass in grams to three significant figures?

When we have ΔH = - 802.3KJ, Negative charge so we can treat the heat as a product of the reaction as the following:
CH4(g) + 2O2(g) → CO2(g) + 2H2O + 802.3KJ
when the enthalpy change is quoted per mole. and  1mole of CH4 give 802.3KJ
1molCH4→802.3KJ
       ←  269 KJ
So how many moles of CH4 if 269 KJ is generated??
moles of CH4 = 269KJ*1mol / 802 = 0.33 mol
and when we have the molar mass of CH4 = 16, we can get the mass from this formula:
 Mass of CH4 = no of moles* molar mass
                        = 0.33 * 16 = 5.24 g

That is a lot of moles that you have

The answer to your question would be c. mineral oil