Adevice has an ip address of 10.1.10.186 and a subnet mask of 255.255.255.0. what is true about the network on which this device resides?
only the last number of each ip address will be unique
only the last two numbers of each ip address will be unique
only the last three numbers of each ip address will be unique
all four numbers of each ip address will be unique

Only the last number of each IP address will be unique

Explanation:

Subnet Mask is used to identify the two parts of the IP address. One is the network part that should be same for one network, and other is host part that will vary with number of computer or devices that are connected to the network.

Subnet mask is 32 bit address that are divided in 4 equal parts of 8 bits. Each 8 bit converted to decimal by varying different bits to generate 256 different decimal number combinations. It means we can vary the address range between 0 to 255. So If any 8 bit portion is 255 that means, in this section we cannot add host address.

For Example

In given case,

Subnet Mask = 255.255.255.0

That means first three portions are fixed and has been allocated for network part.  

The forth portion is 0 that means we can change this portion in IP address up to 255 different addresses.

So the IP address that is given can be vary as:

10.1.10. 186

10.1.10 This portion is network portion, this cannot be vary.

only the number 186 is the unique address that is particularly assigned to the devices and is vary between 0 to 255.