which one's infra rays wavelength are longer, sun or human body?
What do you mean by "infra" rays?? The only "infra" I know applied to wavelength is infrared radiation which has a fixed range of wavelengths no matter where it comes from.
Waves are basically classified on the basis of wavelength ( or frequency ). Infra-red rays is the name for the rays having a particular range for wavelengths. So, it doesn't matter what the source of the rays is. If the wavelength falls in the range, they are called infra-red rays.
This sounds like one of those "flawed" questions that come from a lower-level (elementary or junior high) textbooks. I'm guessing that what the question is getting at is:
"which produces more high-energy infra-red rays, the sun or a human body." I'm sure you could guess which one.
THen, what you need to know is that "high energy" infra-red is "shorter wavelength" infra red. Take it from there.
Separate names with a comma.