The electromagnetic spectrum classifies waves based on their wavelength or frequency. The approximate wavelength ranges are:

• Microwaves: $0.1 \text{ m}$ to $1 \text{ mm}$
• Infrared: $1 \text{ mm}$ to $700 \text{ nm}$
• Ultraviolet: $400 \text{ nm}$ to $1 \text{ nm}$
• Gamma rays: $< 10^{-3} \text{ nm}$

Since wavelength decreases as frequency increases, the correct order from longest to shortest wavelength is: Microwave $>$ Infrared $>$ Ultraviolet $>$ Gamma rays .