Which of the following is the most granular level of the Spark execution hierarchy?

The Spark execution hierarchy from broadest to most granular is: Application > Job > Stage > Task. A task operates on one partition of data and is the smallest schedulable unit. Every other option in this question represents a higher-level or infrastructure concept, not a finer-grained execution unit.

An executor is an infrastructure component that runs tasks - it sits above tasks in the hierarchy.

A node is the physical or virtual machine hosting executors - it is not part of the logical execution hierarchy.

A job is a higher-level grouping of stages, which themselves contain multiple tasks.

A slot represents execution capacity within an executor - it is a resource concept, not a distinct level in the execution hierarchy.