Pls help. :) The boxes show five different substances, A, B, C, D and E.
O and represent atoms of different compounds.
(a) Which box contains a substance that is only one compound?
(b) Which box contains a substance that is a mixture of an element and a
compound?

Which statement is true about the model of the electromagnetic spectrum a: it change the frequencies of light. b: it compare wavelengths of light. c: the color of light waves can be changed using the model. d: the intensities of light waves can be decreased using the model.