This is the 14843rd most frequent German word.
radikal
Radikal: Extreme or far-reaching in effect, change, or approach.
In this sentence, 'radikales' is used as an attributive adjective to describe the behavior as being unconventional or extreme.
Sein radikales Verhalten überraschte alle.
His radical behavior surprised everyone.
'Radikale' functions as an adjective to emphasize that the solutions are extreme or fundamental in addressing the issues.
Manchmal sind radikale Lösungen notwendig, um Probleme zu lösen.
Sometimes radical solutions are necessary to solve problems.
Here, 'radikal' is used as an adjective to describe changes that are fundamental or extreme in nature.