Which expression is used to apply the splat operator to return multiple EBS volume IDs?

The expression that correctly applies the splat operator to return multiple EBS volume IDs is constructed as follows: aws_instance.example.ebs_block_device[*].id. This syntax utilizes the splat operator, indicated by the [*], to gather all the id attributes from the ebs_block_device list associated with the aws_instance.example.

When dealing with collections in Terraform, the splat operator allows you to extract specific attributes from a list, yielding a new list of those attributes. In this case, it extracts the id field from each EBS block device defined in the ebs_block_device attribute of the aws_instance resource. This results in a list of EBS volume IDs that can be easily manipulated or referenced elsewhere in your Terraform configuration.

The other options do not conform to the correct usage of the splat operator or the structure of the aws_instance resource and its attributes. Therefore, the choice that uses the correct syntax for extracting multiple IDs from the list of EBS volumes is indeed the third option.