MCQ question help needed !

Question

MCQ  question help needed !

aminamoazzam · Answer

this is the question .. 
the ans is  B .. but why ? can somebody explain ..

anonymous · Answer

A is wrong because by adding manganese (IV) oxide you're just speeding up the reaction but the oxygen produced will be the same

anonymous · Answer

Note manganese(IV)oxide is a catalyst

anonymous · Answer

Water is already a product form of hydrogen peroxide water is only decomposed by electrolysis which is not happening because you're heating h2O2 right?
 So C is not right D is just increasing the rate of reaction again 
B is correct because only small amount of h2O2 is given notice the curve slightly about curve X? Which indicates a little h2O2 has been added to increase the volume of Oxygen.

anonymous · Answer

It takes more time for the reaction to complete because catalyst is limiting as substrate has been added