I. The colour of light depends on its frequency II. When white light is dispersed by a triangular prism, yellow is deviated more than green III. Rainbows ar...

Answer Details

Each statement has to be tested separately against the physics of dispersion.

1. Colour depends on frequency. Correct. Frequency is the property of a light wave that does not change when the light passes from one medium into another; wavelength and speed both change since \(v = f\lambda\). Because the sensation of colour is unchanged when light travels from air into water or glass, colour must be tied to frequency rather than to wavelength in a particular medium.
2. Yellow deviated more than green by a prism. Incorrect. Deviation by a prism increases as the refractive index of the glass for that light increases, and the index rises as wavelength falls. Green (about \(510\,\text{nm}\)) has a shorter wavelength than yellow (about \(580\,\text{nm}\)), so green has the larger index and is deviated more, not less. The order of increasing deviation is red, orange, yellow, green, blue, indigo, violet, with violet bent most.
3. Rainbows form when rain falls heavily. Incorrect as stated. A rainbow requires sunlight entering water droplets, refracting, reflecting internally once at the back of the drop, and refracting again on leaving, with the observer standing with the Sun behind and the drops in front. Fine drizzle or spray from a waterfall or hose produces a rainbow perfectly well, while heavy rain with a fully overcast sky produces none because no direct sunlight reaches the drops. Heaviness of the rain is not the condition; sunlight plus suspended droplets is.

Only the claim about frequency survives, so the correct response is the one that accepts statement I alone.

The misconception worth correcting is the assumption that longer-wavelength light bends more, which reverses the whole dispersion sequence. Anchor it with one fact: red is deviated least, violet most, because \(n\) is largest for the shortest wavelength. That single rule settles most prism and dispersion questions in an examination.