In a spontaneous reaction-
a. the reaction happens very quickly
b. additional heat is required to make it occur
c. no additional heat is required to make it occur
d. additional heat is absorbed from the environment

C. No additional heat is required to make it occur

Explanation:

A reaction is said to be spontaneous if it can occur on its own. Spontaneous reactions do not require additional energy or heat from other sources to occur.

A spontaneous reaction leads to an increase in the disorderliness of a system.

We can use the free energy change of a system which measures the energy of a system used to useful work to predict the spontaneity of a reaction.

If the Free energy change is negative the reaction is said to be spontaneous or feasible.