Answer: Option (c) is the correct answer.
Step-by-step explanation:
A spontaneous reaction is a reaction which occurs on its own without any intervention or outside force helping in initiation of the reaction.
A combustion reaction is the reaction in which a compound reacts with oxygen atom resulting in the formation of water and carbon dioxide gas.
A physical reaction is a reaction in which there occurs no change in chemical composition of a substance.
Activation energy is the reaction in which minimum amount of energy is required to carry out a reaction. More is the activation energy of a reaction slower will be the rate of reaction, therefore a catalyst is required to increase the rate of reaction.
Thus, we can conclude that spontaneous reaction is the type of reaction that occurs without being started by some outside force.