Do Capacity Reservations guarantee lower pricing like Reserved Instances?

No, Capacity Reservations do not guarantee lower pricing like Reserved Instances (RIs).

Can an EC2 instance launched into an Availability Zone with unused Capacity Reservations fail to use the reservation?

Yes, an EC2 instance can fail to use an unused Capacity Reservation in the same Availability Zone if certain matching criteria are not met.

Can an instance type mismatch prevent it from using an available Capacity Reservation?

Yes, an instance type mismatch can absolutely prevent an EC2 instance from using an available Capacity Reservation.

Will a Capacity Reservation still incur charges even if no instance is using it?

Yes, a Capacity Reservation will still incur charges even if no instance is using it.

Which EBS volume type is the most cost-effective for infrequently accessed data?

Cold HDD (sc1)