At 25°c 12 m h202 is decomposed after 30 minutes the concentration of the h2o2 is found to be 9.5 m what is the average reaction rate for this decomposition reaction.

The decomposition reaction of hydrogen peroxide:
2 H₂O₂(aq) →  2 H₂O(l) + O₂(g)
The order of reaction is : first order reaction.
[H₂O₂]₀ = 12 M at time = 0
[H₂O₂] = 9.5 M at time = 30 minutes
Average reaction rate = - (Δ[reactants] / Δt) 
                   = - (final reactants conc. - initial reactants conc.) / Δt
                   = - (9.5 M -12 M) / (30 min - 0 min) 
                   = 0.083 mol / L.min

The answer is 4 i don't know if its right let me see.

Polymerization reaction