Solution:
In all other pairs, second is the head of the first.

Solution:
All other letters are vowels.

Solution:
All except Plastic are biodegradable materials.

Solution:
All other groups end with a vowel.

Solution:
In all other groups, the first two letters are alternate letters of the alphabet, while second and third letters occupy the same positions from the beginning and the end of the alphabet respectively.

Solution:
All except New York are capital cities.

Solution:
All except Archaeology are branches of Biology.