Which color of light is diffracted at a greater angle from a diffraction grating, red or yellow?

The color of light that will be diffracted at a greater angle from a diffracting grating is THE YELLOW COLOR.
This is because, the degree of diffraction depend on the wavelength of light and light color with shorter wavelength are diffracted at a larger angle than those with longer wavelengths. The wavelength of the yellow color is much more smaller than that of the red color.

Yes you are correct use the scientific method