Solution:
All except Butterfly are birds, while butterfly is an insect.

Solution:
In all other pairs, second is the place where first works.

Solution:
All except Cat are rodents.

Solution:
All except Cot are parts of bed-spread.

Solution:
All except Igloo are types of boats, while igloo is a kind of house found in polar regions.

Solution:
All except Mob represent well-organised groups.

Solution:
Mercury is the only liquid metal in the group.