The capability described-administrators instantly provisioning servers, storage, and compute through a web portal without needing the provider to manually intervene-is the NIST cloud characteristic called on-demand self-service. In NIST's cloud computing model, on-demand self-service means a consumer can unilaterally provision computing capabilities (such as server time and network storage) as needed automatically, without requiring human interaction with each service provider.
The scenario explicitly highlights that the admins can scale resources "instantly" through a dashboard and that there is "no manual involvement from the cloud provider." That is exactly what on-demand self-service captures: rapid provisioning driven by the customer through automated orchestration and APIs/portals.
Why the other options are not the best match:
Broad network access (D) means cloud capabilities are available over the network and accessed through standard mechanisms by heterogeneous platforms (mobile, laptops, workstations). While the dashboard is accessed over the network, broad access is about reachability and standard access mechanisms, not the self- provisioning behavior.
Resource pooling (C) refers to the provider's multi-tenant model where physical/virtual resources are pooled and dynamically assigned; it explains how the provider can offer elasticity, but the user-facing "provision it yourself" aspect is on-demand self-service.
Measured service (B) refers to metering and monitoring resource usage for billing/optimization; it doesn't explain instant self-provisioning.
Therefore, the characteristic is A. On-demand self-service.