This reaction obeys the law of conservation of mass.
Explanation:
In the burning reaction, methane (CH₄) react with oxygen (O₂) to produce carbon dioxide (CO₂) and water (H₂O):
CH₄ + 2 O₂ → CO₂ + 2 H₂O
Now we calculate the number of moles of methane and carbon dioxide:
number of moles = mass / molar weight
number of moles of methane = 10 / 16.04 = 0.62 moles
number of moles of carbon dioxide = 27 / 44.01 = 0.61 moles
From the chemical reaction we see that 1 mole of methane produces 1 moles of carbon dioxide so 0.6 moles of methane produces 0.6 mole of carbon dioxide. This reaction obeys the law of conservation of mass because the mass of reactants is equal to the mass of products.