KClO3 on heating decomposes into KCl and O2. If some MnO2 is added the reaction goes much faster because:
(a) MnO2 decomposes to give oxygen
(b) MnO2 provides heat by reacting
(c) better contact is provided by MnO2
(d) MnO2 acts as a catalyst
(d) MnO2 speeds up the reaction.