Final answer:
Option (A), A rainbow's spectrum is arranged by wavelength, with red having the longest wavelength. Dispersion spreads white light into a spectrum of colors, forming the rainbow's sequence from red to violet, as remembered by the mnemonic ROY G BIV.
Step-by-step explanation:
A rainbow is a spectrum arranged by wavelength, with red having the longest wavelength. In the visible light portion of the electromagnetic spectrum, a rainbow of colors is displayed, which includes violet, blue, green, yellow, orange, and red. Red, at one end of the spectrum, has the longest wavelength, and violet has the shortest. The dispersion of white light into its full spectrum of colors is what creates a rainbow. When light passes through a dispersing object like a prism or a droplet of water, the differing wavelengths are spread out and become visible to the human eye as the sequence of colors we associate with a rainbow.
The mnemonic ROY G BIV stands for Red, Orange, Yellow, Green, Blue, Indigo, and Violet, representing the main colors of visible light from longest to shortest wavelength. Therefore, the correct answer to the question is a) Wavelength.