The velocity of propagation of radio frequency energy in free space is:

Radio frequency energy consists of electromagnetic waves, which travel at the speed of light when moving through a vacuum or free space. In the metric system, the speed of light is approximately 300,000,000 metres per second, which simplifies to 300,000 kilometres per second. Distractors in these types of questions often mix metric and imperial units. For example, 186,000 is the correct number if the units were miles per second, but since the options are in kilometres per second, 300,000 is the only correct choice.