To find the concentration of H2O after 10 seconds, we first need to determine how much the concentrations of H2 and O2 change during this time. Since the reaction rate is given, we can use it to calculate the change in concentration for each reactant.The balanced chemical equation is:2H2 g + O2 g -> 2H2O g The stoichiometry of the reaction shows that 2 moles of H2 react with 1 mole of O2 to produce 2 moles of H2O. Therefore, the rate of change in concentration for H2 is twice that of O2, and the rate of change in concentration for H2O is the same as that of H2.Given the reaction rate of 0.12 M/s for O2, we can find the rate of change in concentration for H2 and H2O:Rate of change in concentration for H2 = 2 * rate of change in concentration for O2 = 2 * 0.12 M/s= 0.24 M/sNow, we can find the change in concentration for each reactant and product after 10 seconds:Change in concentration for H2 = rate of change in concentration for H2 * time= 0.24 M/s * 10 s= 2.4 MChange in concentration for O2 = rate of change in concentration for O2 * time= 0.12 M/s * 10 s= 1.2 MChange in concentration for H2O = rate of change in concentration for H2O * time= 0.24 M/s * 10 s= 2.4 MNow, we can find the final concentrations of each species:Final concentration of H2 = initial concentration of H2 - change in concentration for H2= 0.5 M - 2.4 M= -1.9 M Since the concentration cannot be negative, it means that all the H2 has been consumed and the final concentration is 0 M Final concentration of O2 = initial concentration of O2 - change in concentration for O2= 0.2 M - 1.2 M= -1.0 M Since the concentration cannot be negative, it means that all the O2 has been consumed and the final concentration is 0 M Final concentration of H2O = initial concentration of H2O + change in concentration for H2O= 0 M + 2.4 M= 2.4 MSo, the concentration of H2O after 10 seconds is 2.4 M.