To determine which graph represents exponential decay, let's quickly define it: Exponential decay is when a function decreases rapidly at first, then levels off toward zero as $x$ increases. This happens for functions of the form $y = a e^{-kx}$, where $a > 0$ and $k > 0$, or more generally for forms like $y = a \left(\frac{1}{b}\right)^x$ where $0 < b < 1$.

Now, let's analyze the graphs in your image:

1. Graph 1 (Top graph): This is a linear graph, not exponential, as it shows a straight line.
2. Graph 2 (Second from the top): This graph increases slowly, indicating it might represent exponential growth, not decay.
3. Graph 3 (Third graph): This graph starts high and decreases rapidly, flattening out as $x$ increases. This matches the behavior of exponential decay.
4. Graph 4 (Bottom graph): This is also an increasing curve, suggesting it represents exponential growth.

Therefore, Graph 3 (third from the top) represents exponential decay.

Would you like further details or explanations?

Here are 5 questions to deepen your understanding:

1. What is the general form of an exponential decay function?
2. How can you differentiate between exponential growth and decay by looking at their graphs?
3. What are the real-world applications of exponential decay?
4. Can exponential decay functions ever reach zero?
5. How does the rate of decay change as the value of the exponent increases?

Tip: Exponential decay is characterized by a base between 0 and 1, while growth has a base greater than 1.