Solution:
All except Delicious represent tastes recognised by the human tongue.

Solution:
All except Direct are synonyms.

Solution:
All except Stethoscope are optical instruments.

Solution:
Mercury is the only metal in the group.

Solution:
All except Bunker are terms associated with hockey, while bunker is associated with polo.

Solution:
All except Deuce are terms associated with cricket.

Solution:
All except Oasis are features related to sea, while oasis is related to desert.