Answer:
A. Irreversible is the correct answer.
Step-by-step explanation:
A reaction that can't be undone is called Irreversible.
This indicates that in the irreversible reaction changes are permanent that cannot be undone.
In an irreversible reaction, reactants react to produce products and it cannot return back into the reactants.
In the case of an irreversible reaction, once the chemical properties of the substance changed, it converts different substances. Thus, it cannot revert to its initial state.
We cannot change the new substances obtained back into the primary substances again.
Rusting is an example of an irreversible reaction.