In a zero-order reaction, 47.5% of the reactant remains at the end of 2.5 hours. The amount of reactant consumed in one hour is:

21%

In a zero-order reaction, the rate of reaction is independent of the concentration of the reactant. This means that the same amount of reactant is consumed per unit of time throughout the reaction.

Given that 47.5% of the reactant remains at the end of 2.5 hours, it implies that \(100\% - 47.5\% = 52.5\%\) of the reactant has been consumed after 2.5 hours.

To calculate the amount of reactant consumed in one hour, we can use the concept that the reaction proceeds at a constant rate.

Amount consumed in 2.5 hours = \(100\% - 47.5\% = 52.5\%\)

Amount consumed in 1 hour = \(\frac{{52.5\%}}{{2.5 \text{ hours}}} \times 1 \text{ hour}\)

Calculating the value:

Amount consumed in 1 hour = \(\frac{{52.5\%}}{{2.5}} \times 1 = 21\%\)

Therefore, the amount of reactant consumed in one hour is 21%.

Hence, the correct answer is option (4) 21%.