It depends on whether you are subnetting or not. If not, the default subnet mask would be 255.255.255.0
The correct term is subnet mask instead of subnet mass. A subnet mask separates an IP address into the host address and the network address. It is a 32-bit number that can mask an IP address.
There isn't just a single subnet mask that could be used for that address. The default subnet mask would be 255.0.0.0, but there could be others if the network is subnetted.
Because each IP defines certain subnet mask.
The Method used for changing your subnet mask would be based on what platform your using and its installed operating system.
It does not require a subnet mask.
The address you gave is not an IP address; it has the appearance of a subnet mask. It could be a class A or class B subnet mask.
If this is a default subnet mask, then it would be a class C subnet mask. If you are subnetting a network and this is not the default subnet mask, then it could be either a class A or class B.
No, all subnets must use the same subnet mask
The default subnet mask has a standard size. The custom subnet mask allows you to make subnets that are smaller or larger than the default.
2 given subnets
255.255.255.0
255.255.255.0