Final answer:
The given statements about waves are mixed with truths and falsehoods. A standing wave is created by opposite-direction waves, while wave amplitudes can add up regardless of propagation direction. Pebble-created ripple waves and superposition with different frequencies are both true scenarios.
Step-by-step explanation:
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. Instead, a standing wave is formed when two identical waves traveling in opposite directions meet and interfere with each other.
For the second part, the statement that the amplitudes of waves add up only if they are propagating in the same line is also false. Waves can interfere and their amplitudes can add up as long as they meet, regardless of the direction in which they are propagating.
Regarding a pebble dropped in water, this action creates a pulse wave, so this statement is true. A pulse wave is a single disturbance that moves through a medium, such as the ripples created in water by a pebble.
The amplitude of one wave being affected by the amplitude of another wave only when they are precisely aligned is true. This condition describes constructive interference, where waves that are in phase will combine to produce a greater amplitude.
Finally, the statement that waves can superimpose if their frequencies are different is true. Superposition of waves does not require identical frequencies, though the resultant wave pattern might be complex.