Answer: To extend the functionality of pandas to big data

The Pandas API on Spark, also known as Koalas, is designed to extend the familiar pandas functionality to big data environments, leveraging Spark's distributed computing capabilities. This allows data scientists to use pandas-like operations on datasets that are too large for a single machine's memory, without needing to learn a new API. It does not aim to replace PySpark (making option B incorrect), nor is it a new package (option A is incorrect). While Spark does provide scalable data structures, the primary purpose of the Pandas API on Spark is not just to provide these structures (option D is incorrect), but to extend pandas functionality to big data.

Author: LeetQuiz Editorial Team