Which purchase option is the MOST cost-effective?

Explanations:

On-Demand Instances are billed at a fixed hourly rate and are suitable for applications with unpredictable workloads but are generally more expensive for long-running tasks compared to other options.

Reserved Instances require a commitment for a one- or three-year term, making them less cost-effective for short-term usage like the 2-hour duration specified.

Dedicated Instances provide physical server isolation but come with higher costs compared to standard EC2 pricing. This option is not optimal for a short, stateless application.

Spot Instances allow users to bid on unused EC2 capacity, which can significantly reduce costs. For a stateless application that can be interrupted and run for a short duration, this is the most cost-effective option.