The relationship between "Propensity" and "Tendency" is that they are synonyms, meaning they have similar meanings. Therefore, to determine the corresponding pair from the options, we need to find two words that are also synonyms.
Prologue : Epilogue - These terms are antonyms; a prologue is an introduction, whereas an epilogue is a conclusion.
Master : Slave - These are also antonyms; they describe opposite positions in a hierarchy.
Audacity : Impudence - Both words indicate a bold or disrespectful behavior, making them synonyms.
Conduct : Immortality - These words do not share a synonymous relationship.
Based on this analysis, the correct answer is Audacity : Impudence as they share a synonymous relationship like "Propensity" and "Tendency".