A certain chemical reaction decreases the concentration of a...

Question Analysis
This question tests the student's ability to write the function expression for exponential decay. The problem provides the initial concentration and the decay factor.

Key Concept Explanation
In an exponential decay function , the base is a fraction between 0 and 1. For this problem, the concentration decreases by 25% every hour, so .

Step-by-step Solution
1. Identify the initial concentration