26
255.255.0.0 Class B 128.0.0.0 - 191.254.254.254 default subnet 255.255.0.0
10.0.0.0/16 is subnetted, 1 subnets D 10.5.0.0[90/205891] via 192.168.1.2, S0/0/0 10.0.0.0/24 is subnetted, 4 subnets D 10.5.0.0[90/205198] via 192.168.1.2, S0/0/0 10.0.0.0/22 is subnetted, 1 subnets D 10.5.0.0[90/205901] via 192.168.1.2, S0/0/0 10.0.0.0/8 is subnetted, 4 subnets D 10.5.0.0[90/205001] via 192.168.1.2, S0/0/0
65,534
If your address is not subnetted, then the default subnet mask would be used. For this class address, it would be 255.0.0.0
255.255.254.0
Each device can be identified by its IP address (assigned for the network and can be subnetted) and its MAC - which is a device identifier supposedly unique to the device.
You have a class C network connection. Since the subnet mask was not specified I can't tell if it is a traditional class C or if the network has been subnetted.
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.
The subnet id identifies which smaller network within a larger network (the subnetted network) the packet should be delivered to. The subnet id is part of the extended network prefix which is used for routing.
A general industry rule of thumb is to use the first IP address in a range for the default gateway address. That would be .1 for most classful, non-subnetted networks.
The gateway address can only be assigned after the subnet mask is declared. You really can't define both from just an IP address of a single node. The network may or may not be subnetted.
Specialized Device for exchanging data amongst class based Networks & Subnetted (multiple parts of one network) is Router.