Among the options provided, microwaves have the longest wavelength. Here’s a comparison of the wavelengths of the options:
- Gamma rays: Very short wavelengths (less than 0.01 nanometers).
- X-rays: Short wavelengths (approximately 0.01 to 10 nanometers).
- Infrared waves: Longer wavelengths (approximately 700 nanometers to 1 millimeter).
- Microwaves: Even longer wavelengths (approximately 1 millimeter to 1 meter).
Therefore, the correct answer is microwaves.