You are planning to use the AWS classic load balancer in AWS. You are preparing the subnets which will be used in the load balancer. Which of the following bitmask is the minimum which is required for the subnet in order to be used with the Load Balancer

Answer options:

A./30
B./29
C./28
D./27

Answer – D
This is mentioned in the AWS documentation
To ensure that your load balancer can scale properly, verify that each subnet for your load balancer has a CIDR block with at least a /27 bitmask (for example, 10.0.0.0/27) and has at least 8 free IP addresses. Your load balancer uses these IP addresses to establish connections with the instances.
For more information on setting up the instances in an ELB, please visit the below link:
http://docs.aws.amazon.com/elasticloadbalancing/latest/classic/elb-backend-instances.html