Answer
The radiation in part a) is not visible to the human eye.
The radiation in part b) is visible to the human eye.
Work Step by Step
A radiation is only visible to human eye if it is in the wavelength range of the visible light, which is from $400nm$ to $750nm$.
*Part a):
The wavelength of radiation is $10\mu m$, therefore $\lambda = 10\mu m=10000nm$.
Since a radiation with a wavelength of $10000nm$ is not in the wavelength range of the visible light, it is not visible to human eye.
*Part b):
The wavelength of radiation is $545nm$. Therefore, it is in the wavelength range of visible light, which means it is visible to the human eye.
