Q19 (20 points) What are Docker images and Docker containers?

A Docker image is a lightweight, immutable archive file containing all the OS, datafiles, applications, and dependencies needed to run software. A Docker container is the runtime instance created from that image—an isolated, executable unit. Option B correctly reverses the relationship presented in Option A, establishing the proper definition where images are templates and containers are running instances.

Step-by-step Derivation:
Recall the Docker architecture: (1) A Docker image is a blueprint—a static, layered archive file containing the complete filesystem, application code, libraries, and dependencies. (2) A Docker container is a runtime instantiation of an image—a lightweight, isolated process that executes the image's contents. This is the reverse of the relationship in Option A. Options C and D incorrectly describe images as 'units of software' and containers as 'files,' which inverts both the nature (archive vs. process) and the creation direction (containers don't create images). Option B is the only one that correctly identifies images as archives and containers as executable units derived from those archives.