Question: You have an RGB image that you want to convert to a duotone, but in the image > Mode menu, the Duotone option in grayed out. Why is this happening?

1. You must add a spot color channel first
2. You must remove all existing color by Image > Adjustments > Desaturate first
3. Duotones require a single channel, so you must convert to grayscale first
4. Duotones require two channels, so you must delete one of RGB channels in the Channels panel first

Answer: The correct answer of the above question is Option C:Duotones require a single channel, so you must convert to grayscale first