An office has 8 floors with approximately 30-40 users per floor (CCNA 200-301)

Correct answer: B) ip address 192.168.0.0 255.255.254.0.
Given the requirement to support 40 users per subnet and the need for 8 different subnets, we indeed need to calculate the subnet mask that corresponds to a /23 prefix.

A /23 prefix means that the first 23 bits of the IP address are used for the network part, leaving 9 bits for the host part. In binary, this is represented as 255.255.254.0.

To convert the /23 prefix to a subnet mask:

Convert the prefix length to binary. A /23 prefix means the first 23 bits are set to 1, and the remaining bits are set to 0. In binary, this is represented as 11111111.11111111.11111110.00000000.
Convert each 8-bit binary number to its decimal equivalent. This gives us 255.255.254.0.
Therefore, the subnet mask that corresponds to a /23 prefix is 255.255.254.0.

However, based on the options provided in your question, the correct answer is:

B) ip address 192.168.0.0 255.255.254.0

This option matches the calculated subnet mask for a /23 prefix, which is the most efficient way to use address space for the given scenario, accommodating 40 users per subnet and allowing for 8 different subnets.