Which Amazon EC2 instance pricing model can provide discounts of up to 90%?

Explanations:

Reserved Instances provide discounts of up to 75% for long-term commitments but not up to 90%.

On-Demand instances are charged at a fixed rate with no discount based on time of use.

Dedicated Hosts provide physical servers but are not designed for cost savings.

Spot Instances offer discounts of up to 90% for unused EC2 capacity, making them highly cost-effective.