What is the reactant in coke and mentos?

In the reaction between Coke and Mentos, the primary reactant is the carbon dioxide gas dissolved in the Coke (the beverage). When Mentos candies are added, their rough surface facilitates the rapid release of this gas, leading to a dramatic eruption of foam. The reaction is primarily a physical process rather than a chemical one, as the carbonation rapidly escapes due to the nucleation sites provided by the Mentos.