You created a new VPC with CIDR range 10.10.0.0/16 and a new subnet with CIDR range 10.10.1.0/24. CIDR with /24 comes with 256 IP addresses. When you go to VPC console subnets and look at the newly created subnet, you can only see 251 IP addresses. You have not launched any resources in the newly created VPC. What would have caused this?

Answer options:

A.The first four IP addresses and the last IP address in each subnet CIDR block are reserved by AWS.
B.AWS reserves 5 IP addresses for every VPC and are reserved from first subnet you create.
C.AWS launches monitoring resources on behalf of you in new VPC when first subnet is created which will reserve 5 IP addresses from first subnet.
D.None of the above.

Answer: A
https://docs.aws.amazon.com/AmazonVPC/latest/UserGuide/VPC_Subnets.html#VPC_Sizing
From the above statement, only
Option A is correct.
For Option C, AWS never launches any billable resources without notifying the account owner or administrator on behalf of you.