Have a look at these examples of Movers Speaking test PART 3. Keep in mind that there are many useful expressions you can use for this purpose.
Eg: The dog is different because it is a domestic animal but the lion, the panda, and the bat are wild animals
Here you have an example of a longer description...
Eg: In this group of pictures, the odd one out is the cake because the banana, the pineapple, and the orange belong to the category of fruits but the cake isn't a fruit.
YOUR TURN! GIVE IT A TRY WITH THE FOLLOWING SETS OF PICTURES!