Note: If you are not sure about Subnetting, please read my Subnetting Made Easy tutorial.
Question 1
Explanation
AREA 1 has 500 users but it uses class C which only supports 254 users (from 192.168.1.1 to 192.168.1.254)-> A is correct.
AREA 3 also uses class C and as mentioned above it supports 254 users so it is enough for 200 users -> B is incorrect.
In AREA 2 there are only 60 users < 64 = 26 so we can use a subnet mask which has 6 bits 0 -> /26. Of course we can use larger subnets (like /25) for future expansion -> C is correct.
A large network should never use a single network-wide mask. It should be some different subnet masks to make the network flexible and easy to be summarized -> D is incorrect.
For router-to-router connection we should use a subnet mask of /30 which supports 2 hosts per subnet. This subnet mask is ideal for router-to-router connection -> E is correct.
There is no limit for IP to function if we know how to organize our network -> F is incorrect.
Question 2
Explanation
The maximum number of hosts in this question is 50 hosts so we have to use /26 subnet mask or above.
Question 3
Explanation
To support 300 workstations in a single broadcast domain, we need to use a subnet mask which supports 512 hosts = 29 -> /23 or 255.255.254.0 in decimal form -> A is correct.
If we use 48-port switches we need 300/48 = 6.25 -> seven 48-port switches are enough because we also need trunking between them -> D is correct.
We only need one router interface and it is connected with one of seven switches -> E is correct.
Question 4
Explanation
/19 = 255.255.224.0. The fast way to find out this subnet mask is to remember /16 = 255.255.0.0 and we need 3 more bits 1 for 3rd octet: 1110 0000 which is 224.