The figure (examples ) of the question is attached below.
Answer: The answer is prism.
Explanation:
When a ray of white light passes through the prism it separates into many colors or different wavelength of light is seen.
This phenomenon is known as diffraction .In the visible wavelengths of the  electromagnetic spectrum, red, is diffracted most and violet is diffracted lowest due to shortest wavelength.
It appears like a rainbow of 7 colors because it is white light that diffracts into 7 colors after passing a prism.
