The correct option is Elasticity. Elasticity is the architectural characteristic that enables infrastructure to expand automatically during traffic spikes and to contract when demand falls so capacity matches fluctuating demand and costs align with usage.

Elasticity works by allowing resources to be provisioned and released dynamically so the system remains resilient under bursty traffic while avoiding unnecessary expense. Cloud providers expose services and APIs that implement this principle so teams can focus on application behavior rather than manual capacity planning.

Vertical scaling refers to increasing the size of a single server and it is not unique to the cloud and it has practical limits which make it unsuitable as the general cloud characteristic being asked for.

AWS Auto Scaling is a specific service that can implement the architectural concept but the question asks for the characteristic rather than a particular tool so the service answer is not correct here.

Monolithic architecture is an application design style and it is not a cloud characteristic. Cloud native designs usually favor modular or microservices approaches to enable horizontal scaling and agility.

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