Wave Properties and Phenomena

Having different amplitudes wouldn't create a standing wave.
Standing waves are characterized by nodes (points of no motion) and antinodes (points of maximum displacement).
Analogy: Strings on a guitar demonstrate standing waves.

Diffusion refers to the scattering of light in different directions.
Light rays reflecting from a surface do not remain parallel after interacting with the surface.

Refraction is the bending of light as it passes through a boundary with a new medium.
Example: Option A in the context is refraction.

The frequency of a sound wave (pitch) changes when the source is moving relative to the observer.

A car's horn produces a constant frequency of $350$ Hz.
If the car moves toward a stationary observer, the detected frequency increases.
This is because the sound waves are bunched up in front of the moving car and spread out behind it.
Velocity is a vector quantity, so the velocities of the car and sound wave add together.
If the source is stationary, there is no change in frequency and no bunching or spreading of waves.
Acceleration would have the same effect as if it was stationary.

Imagine a siren mounted on a car moving at $30$ meters per second.
The velocity of sound is $343$ meters per second.
Since the car is traveling in the same direction as the sound waves, the waves are bunched up in front of the car and spread out behind it.

The diagram represents a ray of light passing from medium x, with a given index of refraction.