The speed of light in a vacuum isGroup of answer choices768 km per hour300,000 km per second186,000 miles per hour.343 meters per secondnot given.

To find the correct answer about the speed of light in a vacuum, let's evaluate the given choices individually.

1. 768 km per hour: This is much lower than the actual speed of light.
2. 300,000 km per second: This is widely recognized as the approximate speed of light in a vacuum; it is actually around 299,792 km per second but often rounded to 300,000 km per second for simplicity.
3. 186,000 miles per hour: This is also a commonly accepted approximation, as it converts to about 299,792 km per second.
4. 343 meters per second: This speed pertains to sound in air at room temperature, not light.
5. Not given: This choice implies that none of the other options are correct, which is not the case.

Final Answer

The correct answer is 300,000 km per second.