Final answer:
Svante Arrhenius defined acids as substances that release hydrogen ions (H+) in water and bases as those that release hydroxide ions (OH-) in water, with the correct answer to the student's question being option a).
Step-by-step explanation:
The theoretical definition of acids and bases according to Svante Arrhenius is that an acid releases hydrogen ions (H+) in water, while a base releases hydroxide ions (OH-) in water. Therefore, the correct answer to the question is option a) Acids release hydrogen ions in water; bases release hydroxide ions in water. The Arrhenius theory was a significant development in the study of acid-base reactions and contributed to Arrhenius being awarded the Nobel Prize in Chemistry in 1903.