Which Azure compute service is designed for running parallel batch-processing jobs on demand?

Azure Batch is the correct answer because it is specifically designed to run large-scale parallel and high-performance computing (HPC) applications efficiently in Azure. It manages a pool of virtual machines, schedules tasks, and handles all the infrastructure required for batch processing, making it ideal for on-demand batch jobs. Azure Functions is a serverless compute service for event-driven, short-lived tasks, not typically for large-scale parallel batch processing. Azure App Service is a platform for hosting web applications, APIs, and mobile backends. Azure VM Scale Sets are used to deploy and manage a set of identical, auto-scaling virtual machines, but they don't inherently provide the job scheduling and task management capabilities that Azure Batch offers for parallel processing.