Final answer:
It is true that waves with different frequencies can superpose. The amplitude compound of waves does not require precise alignment. A pebble creating ripples in water is an example of a pulse wave, while a standing wave is formed by two waves moving in opposite directions.
Step-by-step explanation:
The statement that waves can superimpose if their frequencies are different is true. Superposition is when two or more waves overlap, and their effects combine. The combined wave at any point is the sum of the individual waves' amplitudes at that point. This can happen regardless of whether the waves have the same or different frequencies.
The claim that the amplitude of one wave is affected by the amplitude of another wave only when they are precisely aligned is false. Wave amplitudes can combine (through superposition) when they meet, not just when they are perfectly aligned. The resultant amplitude is a vector sum of the individual amplitudes, which means it depends on both the magnitude and the phase of the interacting waves.
The statement a pebble dropped in water is an example of a pulse wave is true. A pulse wave is a single disturbance that travels through a medium, and a pebble dropped in water creates a disturbance that propagates outward as a pulse wave.
In contrast, the statement that a standing wave is a superposition of two identical waves that are in phase and propagating in the same direction is false. A standing wave is actually formed by the superposition of two waves with the same frequency and amplitude, traveling in opposite directions, that interfere with each other.