To determine which isotope of gallium ($\ce{Ga-69}$ or $\ce{Ga-71}$) is more prevalent in a gallium LED, we need to consider the average atomic mass of gallium, which is $69.72 \, \text{amu}$.

The atomic mass of an element is the weighted average of the masses of its isotopes, based on their natural abundances. Since the atomic mass of gallium is closer to $69$ than to $71$, this suggests that the isotope $\ce{Ga-69}$ is more abundant.

Here's the reasoning:

• The atomic mass of $\ce{Ga-69}$ is $69 \, \text{amu}$.
• The atomic mass of $\ce{Ga-71}$ is $71 \, \text{amu}$.
• The average atomic mass is $69.72 \, \text{amu}$, which is closer to the mass of $\ce{Ga-69}$, indicating that $\ce{Ga-69}$ must be more prevalent than $\ce{Ga-71}$.

Thus, the correct answer is: (Choice A) $\ce{Ga-69}$

Would you like more details or have any questions on this? Here are a few related questions you could explore:

1. What is the significance of isotopes in chemical reactions?
2. How is the atomic mass calculated from isotopes and their abundances?
3. Why is gallium used in LEDs and other electronics?
4. What are the physical properties of gallium?
5. How are the isotopes of gallium separated or enriched for industrial use?

Tip: When you see an average atomic mass that’s closer to one isotope’s mass, you can infer that this isotope is more abundant in nature.