A : The soap film in sun light is colourful.
R : Thin films produce interference of light.

Options

A. Both A and R are true and R is the correct explanation of A
B. Both A and R are true and R is not the correct explanation of A
C. A is true and R is false
D. Both A and R are false

Answer

To solve the question, we need to analyze the assertion and the reason provided:

**Assertion (A):** The soap film in sunlight is colourful.
**Reason (R):** Thin films produce interference of light.

### Step-by-step Solution:

1. **Understanding the Assertion:**
- When sunlight hits a soap film, it appears colorful. This is a common observation and can be attributed to the phenomenon of light interference.

2. **Understanding the Reason:**
- Thin films, like soap films, consist of two surfaces (the top surface and the bottom surface). When light strikes the film, some of it is reflected off the top surface, and some passes through and is reflected off the bottom surface.

3. **Interference of Light:**
- The light waves reflected from the two surfaces can interfere with each other. Depending on the path difference between these two waves, they can either constructively interfere (resulting in bright colors) or destructively interfere (resulting in dark regions).

4. **White Light and Color Formation:**
- Sunlight (white light) consists of multiple colors (Violet, Indigo, Blue, Green, Yellow, Orange, Red). When the thin film causes interference, different wavelengths (colors) of light will interfere constructively or destructively at different angles, leading to the appearance of various colors.

5. **Conclusion:**
- Since the soap film displays a range of colors due to the interference of light, both the assertion and the reason are true. Furthermore, the reason correctly explains the assertion.

### Final Answer:
Both the assertion and the reason are true, and the reason correctly explains the assertion.