which graph represents exponential decay?

Explanation:

Step1: Recall exponential - decay property

An exponential - decay function has the form $y = a\cdot b^{x}$, where $a>0$ and $0 < b<1$. Its graph starts high on the $y$ - axis (when $x = 0$, $y=a$) and decreases as $x$ increases, getting closer and closer to the $x$ - axis but never reaching it.

Step2: Analyze each graph

The first graph is a linear function. The second and third graphs are increasing functions, which represent exponential growth. The fourth graph starts at a positive $y$ - value and decreases as $x$ increases, approaching the $x$ - axis, which is characteristic of exponential decay.

Answer:

The fourth graph (from the left)