You are working in a gaming company with four departments that make games for iOS, Android, Windows, and PlayStation. For that, they just recently adopted a hybrid cloud architecture where their on-premise data center is connected to their Amazon VPC. Your VPC is configured with a CIDR block of 10.0.0.0/24 (256 IPs). Your supervisor told you that they need such security in all four departments so that information from one department should not reach other departments. They don’t want to have a new network that can be expensive and will create more overhead. As a Solutions Architect, how will you configure your network to accomplish this requirement?

Answer options:

A.Create four subnets where first one subnet will use CIDR block 10.0.0.0/28 (for addresses 10.0.0.0 - 10.0.0.63), the second subnet will use CIDR block 10.0.0.64/28 (for addresses 10.0.0.64 - 10.0.0.127), third subnet will use CIDR block 10.0.0.128/28 (for addresses 10.0.0.128 - 10.0.0.191), the fourth one will use CIDR block 10.0.0.192/28 (for addresses 10.0.0.192 - 10.0.0.255).
B.Create four subnets where first one subnet will use CIDR block 10.0.0.0/26 (for addresses 10.0.0.0 - 10.0.0.63), the second subnet will use CIDR block 10.0.0.64/26 (for addresses 10.0.0.64 - 10.0.0.127), third subnet will use CIDR block 10.0.0.128/26 (for addresses 10.0.0.128 - 10.0.0.191), the fourth one will use CIDR block 10.0.0.192/26 (for addresses 10.0.0.192 - 10.0.0.255).
C.Create four subnets where first one subnet will use CIDR block 10.0.0.0/32 (for addresses 10.0.0.0 - 10.0.0.63), the second subnet will use CIDR block 10.0.0.64/32 (for addresses 10.0.0.64 - 10.0.0.127), third subnet will use CIDR block 10.0.0.128/32 (for addresses 10.0.0.128 - 10.0.0.191), the fourth one will use CIDR block 10.0.0.192/32 (for addresses 10.0.0.192 - 10.0.0.255)
D.Create four subnets where first one subnet will use CIDR block 10.0.0.0/26 (for addresses 10.0.0.0 - 10.0.0.64), the second subnet will use CIDR block 10.0.0.65/26 (for addresses 10.0.0.65 - 10.0.0.128), third subnet will use CIDR block 10.0.0.129/26 (for addresses 10.0.0.129 - 10.0.0.192), the fourth one will use CIDR block 10.0.0.193/26 (for addresses 10.0.0.193 - 10.0.0.255)
E.The requirement proposed by the supervisor is impossible.

Correct Answer - B 
Option B is CORRECT because to achieve the requirement, you should create four subnets and CIDR 24. After creating four Subnets, it will be CIDR 26, and the range will start from 0 to 63, 64 to 127, 128 to 191, and 192 to 255.
Option A is incorrect because CIDR 28 will result in 16 subnets.
Option C is incorrect because CIDR 32 represents the IP address itself.
Option D is incorrect because CIDR block 10.0.0.0/26 represents 10.0.0.0 - 10.0.0.63 not 10.0.0.0 - 10.0.0.64, then it becomes 65 IP addresses which is incorrect. 
Option E is incorrect because the supervisor`s requirement can be configured.
Refer: https://docs.aws.amazon.com/vpc/latest/userguide/VPC_Subnets.html