Which of the following reactions is not correct

Question:
Which of the following reactions is not correct according to the law of

conservation of mass.

(i) 2Mg(s) + O2(g) →2MgO(s)

(ii) C3H8(g) + O2(g) → CO2(g) + H2O(g)

(iii) P4(s) + 5O2(g) → P4O10(s)

(iv) CH4(g) + 2O2(g) → CO2(g) + 2H2O (g)

Solution:

Option (ii) C3H8(g) + O2(g) → CO2(g) + H2O(g)