Final answer:
The prefix giga- represents 1 billion meters, corresponding to a power of ten as 10⁹.
Step-by-step explanation:
The prefix giga in gigameter represents 1 billion meters, which can be written as a power of ten as 10⁹. So the correct answer to the question is option a. 10⁹. This is because the metric prefix giga- denotes a factor of 10⁹, as seen in expressions like 1 gigameter (1 Gm), which equals 1,000,000,000 meters (10⁹ meters).