Final answer:
The regions of the electromagnetic spectrum should be arranged as microwave < infrared < visible < gamma, in order of increasing frequency.
Step-by-step explanation:
The correct arrangement of the given regions of the electromagnetic spectrum in order of increasing frequency is: microwave < infrared < visible < gamma. This order can be confirmed by consulting diagrams of the electromagnetic spectrum which show that as frequency increases, the type of EM radiation passes from radio waves to microwaves, to infrared, then visible light, followed by ultraviolet, X-rays, and finally gamma rays at the highest frequencies.