Express the equilibrium constant for the combustion of propane in the balanced chemical equation c3h8(g)+5o2((g)+4h2o(g)

According to the balanced equation:
C3H8(g) + 5O2(g) ↔ 3CO2(g) + 4 H2O (g)
      aA    + bB        ↔  cC          +    dD

according to K formula when:
K = concentration of the products / concentration of the reactants

   K = [C]^c[D]^d / [A]^a[B]^b
when [A],[B],[C]and[D] is the concentrations 
and a,b,c and d is the no of moles
∴ K = [CO2]^3[H2O]^4 / [C3H8] [ O2]^5

Your question is not interpreted very well, but as regards what is observed, SO2 is not the formula for sulfur oxide, the formula for sulfur oxide is SO since the valence used in sulfur would be +2 and oxygen -2 therefore the sum of these valences would be equal to zero, therefore it would be the correct thing considering the true equation as SO

Explanation:

There are also sulfur dioxide, or sulfur trioxide, which is usually used in the formation of tertiary salts such as copper sulfate.

sulfur trioxide and sulfur dioxide are synonymous with sulfate or sulphite