Answer
1.06 mm. Microwave.
Work Step by Step
Use Wien’s displacement law, equation 39.21.
$$\lambda_m =\frac{2.90\times10^{-3}m \cdot K}{T}$$
$$\lambda_m =\frac{2.90\times10^{-3}m \cdot K}{2.728K}=1.06\times10^{-3}m$$
This wavelength is in the microwave portion of the electromagnetic spectrum.