In which cloud computing service model does a provider's applications run on a cloud infrastructure and the consumer does not manage or control the underlying infrastructure?

The correct answer is Software as a Service (SaaS). In the SaaS model, the provider hosts applications on a cloud infrastructure, and consumers can access these applications over the internet without needing to manage or control the underlying infrastructure. This allows users to benefit from software applications such as email, customer relationship management (CRM), or office productivity tools, without the complexities associated with hardware and software management.

In contrast, Platform as a Service (PaaS) offers an environment for developers to build and deploy applications while still requiring some level of management and control over the deployed applications. Infrastructure as a Service (IaaS) provides virtualized computing resources over the internet, giving consumers more control and responsibility for managing the infrastructure itself. Public cloud refers more to the deployment model rather than a specific service model, and it can encompass any of these service models. Therefore, in SaaS, consumers are completely hands-off regarding infrastructure management, which is the defining characteristic of this model.