Answer
Arrhenius, a Swedish chemist, played a pivotal role in the early development of physical chemistry alongside Ostwald. His contributions revolve around the revolutionary theory of electrolytic dissociation, which elucidates that when an electrolyte dissolves in a solvent, it breaks up into positively charged ions (cations) and negatively charged ions (anions). This concept revolutionized our understanding of chemical reactions in solutions and laid the foundation for modern electrochemistry.