Which cloud service model primarily places the responsibility for access and administration on the customer?

The correct answer is Infrastructure as a Service (IaaS) because this cloud service model provides users with significant control over the computing resources, including servers, storage, and networking capabilities. In IaaS, the cloud provider is responsible for the underlying infrastructure, while the customer is tasked with managing the operating systems, applications, and any data deployed on that infrastructure. This means the customer has a greater responsibility for access, administration, and security of their systems and data compared to other models.

In contrast, Platform as a Service (PaaS) offers a higher level of abstraction, which abstracts away much of the infrastructure management, allowing customers to focus on application development more than on system administration. Software as a Service (SaaS) places the most responsibility on the provider, with customers generally having limited control over the application and its underlying infrastructure. A Private Cloud is a deployment model rather than a service model and can vary in terms of management responsibilities, often depending on whether it's managed internally or by a third-party provider.