You've loaded a Spark dataframe with data, that you now want to use in a delta table. What format should you use to write the dataframe to storage?

• A. CSV
• B. PARQUET
• C. DELTA
• D. JSON

Answer: (C)

Delta format is used when you want to turn a Spark DataFrame into a Delta table. Delta Lake adds a transaction log on top of Parquet data files, enabling ACID transactions, time travel, schema evolution, and reliable upserts/deletes. The data itself is stored as Parquet, but the Delta format provides the extra metadata layer that coordinates reads and writes. Writing in Delta format ensures you can leverage these Delta features, whereas formats like CSV, JSON, or plain Parquet won’t give you the Delta transaction log and its benefits.