What is the difference between half-duplex and full-duplex transmission modes?

What does the amplitude of a signal measure?

Can we say whether a signal is periodic or nonperiodic by just looking at its frequency domain plot? How?

A color image uses 16 bits to represent a pixel. What is the maximum number of different colors that can be represented?

Which signal has a wider bandwidth, a sine wave with a frequency of 100 Hz or a sine wave with a frequency of 200 Hz?