To find the wavelength at which a blackbody radiates most strongly, we use Wien's displacement law:

λ_max = b / T

where:

* λ_max is the wavelength of peak emission (in meters)

* b is Wien's displacement constant (approximately 2.898 × 10^-3 m·K)

* T is the temperature (in Kelvin)

Given the temperature of 20,000 K:

λ_max = (2.898 × 10^-3 m·K) / (20,000 K)

λ_max ≈ 1.449 × 10^-7 m

This can be converted to nanometers:

λ_max ≈ 144.9 nm

Therefore, a blackbody at 20,000 K would radiate most strongly at approximately 144.9 nanometers, which falls within the ultraviolet region of the electromagnetic spectrum.