Question

Chameleons contain crystals that reflect light and produce colour. Adjusting the spacing between these crystals, they can alter the wavelengths of light reflected, thus changing their skin colour. Based on the above information, we can infer that the change in colour by chameleons is a:

• A. chemical change because change in colour takes place.
• B. chemical change because wavelength of reflected light changes.
• C. physical change because the space between crystals is adjusted.
• D. physical change because light is reflected by crystals.

Hint:

Ask yourself whether any new substance is formed when the chameleon changes colour.

Answer 1

The Correct Option is C

Step 1: Read what the passage says:
The skin of a chameleon has tiny crystals that reflect light. The colour we see depends on the wavelength of the light they reflect.
The chameleon changes the gap between these crystals. A different gap reflects a different wavelength, so the skin shows a different colour.
The passage never says that any new substance is made. Only the spacing of the same crystals changes.

Step 2: Recall the test for physical and chemical change:
In a chemical change a new substance forms. It has new properties and the change is usually hard to reverse. Rusting of iron and curdling of milk are examples.
In a physical change no new substance forms. Only the shape, size, state, arrangement or appearance changes. The change can usually be reversed.

Step 3: Apply the test to the chameleon:
The crystals stay the same crystals. They only move closer together or farther apart.
No new substance is formed, and the chameleon can go back to its old colour by restoring the gap. So this is a physical change.
The reason is that the space between the crystals is adjusted. This matches option C.

Step 4: Why the other options are wrong:
Option A is wrong. A change of colour alone does not prove a chemical change. We need a new substance, and here there is none.
Option B is wrong. The wavelength of reflected light changes only because the spacing changes. A change in wavelength is not a chemical reaction.
Option D is wrong. The change is physical, but the reason is not correct. Crystals reflect light all the time. The colour changes because the spacing changes, not because light is reflected.

Final Answer:
The colour change of a chameleon is a physical change because only the space between the crystals is adjusted. This is option C. \[ \boxed{\text{C}} \]