The correct choice is Per second for an Amazon EC2 instance launched with the Amazon Linux 2 AMI.

AWS bills compute usage for Linux based EC2 instances in one second increments after a 60 second minimum, so Per second reflects the actual billing unit for the instance runtime and gives more precise billing for short lived instances.

Per hour is incorrect because AWS replaced hourly granularity for Linux EC2 instances with per second billing, so the older per hour model no longer applies to current Linux instance pricing.

Per CPU core is incorrect because EC2 pricing is tied to the selected instance type as a whole and not charged by individual CPU cores.

Per GB of EBS storage is incorrect because that unit applies to EBS storage costs and not to EC2 compute billing.

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