Solution
The correct answer is 130.56.155.192
Key PointsWhen the IP address block 130.56.0.0/16 is divided into 1024 subnets, it means that we require 10 more bits for subnetting, which means we need to extend the subnet mask by 10 bits.
The original subnet mask for the /16 network was 255.255.0.0. When we extend by 10 bits, we get a /26 network.
In dotted decimal format, a /26 network's subnet mask is 255.255.255.192. So, our new subnet mask will not have any prefix of the 130.56 network block because those are separate parts of the IP addressing scheme.
For standard subnet masks, first octet would be 255, 255, 255, or 192 (for /26 network).
The network or block assigned is IP specific (130.56.0.0/16), the mask relates to the network + subnet ("slash") size. Here, the subnet mask related to /26 is 255.255.255.192.
Mistake PointsThe correct subnet mask should indeed be 255.255.255.192 when the /16 IP address block is divided into 1024 subnets, resulting in a /26 prefix (16 original + 10 extra to create the subnets).
However, none of the options (130.56.155.192, 130.56.0.255, 130.56.255.255, 130.255.255.255) correspond to valid subnet masks. Official answer is option 4.
