Final answer:
In a zero-order reaction, the reactant decreases at a constant rate over time. After 1 hour, 25% of reactant A is left. Thus, after another hour, no reactant A would be left unreacted.
Step-by-step explanation:
The question refers to the behavior of a zero-order reaction in which a reactant A transforms into product B over time. In a zero-order reaction, the rate of reaction is constant and does not depend on the concentration of the reactant. Therefore, the amount of reactant decreases linearly over time. If after 1 hour, reactant A is 75% reacted, this means that 25% of the initial concentration is left. Since the reaction rate is constant, after another hour (making it a total of 2 hours), an additional 25% of the initial concentration will have reacted, leaving 0% of reactant A unreacted.
It's important to note that this simplification assumes the reaction can proceed until the reactant is entirely consumed, which is theoretically possible in a non-equilibrium scenario.
In reality, other factors could alter the course of the reaction, but based exclusively on zero-order kinetics, no reactant A would remain after 2 hours given the constant rate of reaction.