Final answer:
The correct answer is on-demand scalability, which enables additional resources to be allocated automatically in response to changing demand.
Step-by-step explanation:
The cloud computing feature that allows users to access additional storage, processing, and capabilities automatically without the need for manual intervention from the service provider is known as on-demand scalability. This feature provides flexible resources as the demand increases or decreases, helping to manage workload spikes without upfront investments in infrastructure. Self-service refers to the capability of users to directly manage their cloud services, whereas virtualization is a technology that allows multiple virtual instances on a single physical server. Cloud security encompasses technologies and policies designed to protect data and applications within the cloud.