Which of the following is true about microwaves in unguided media?

The correct answer is 2) They require line-of-sight transmission.   

Concept:

Microwaves are electromagnetic waves with frequencies ranging from roughly 300 MHz to 300 GHz. In unguided media (like air or space), they travel in straight lines.   
Line-of-sight transmission means that there must be a direct, unobstructed path between the transmitting and receiving antennas. Obstacles like buildings, hills, and even heavy rain can significantly attenuate or block microwave signals.
Let's look at why the other options are incorrect:

1. They are slower than radio waves. All electromagnetic waves, including microwaves and radio waves, travel at the speed of light in a vacuum and very close to the speed of light in the atmosphere. There is no significant speed difference between them.   
2. They are not affected by obstacles like buildings or hills. As mentioned earlier, microwaves are indeed affected by obstacles. Their relatively short wavelengths (compared to some radio waves) make them more susceptible to blockage and reflection by such objects.
3. They use fiber optics for data transmission. Fiber optics is a guided medium, where data is transmitted as light pulses through glass or plastic fibers. Microwaves, by definition in this context ("unguided media"), propagate through the air or space without a physical guide.