Six of the 206 bones of human skeleton occur in
A. Skull
B. Middle ear
C. Pectoral girdle
D. Pelvic girdle

Hint:
Organ which has a pair of three bones in the set of two which together form to be known as auditory ossicles. They are very small in size and also known to be the smallest in the whole skeleton system with a very fragile property.

Complete answer:
 Middle ear consists of three bones
These three bones are present in one ear and usually the human body has two middle ears which contribute to having six bones out of 206 bone-in a human skeleton.
 These bones are joint to each other and are very fragile.
 Naming: malleus (hammer), incus (anvil), and stapes (stirrup).
 Malleus is joint to the eardrum on one side and incus on the other side, it is a fragile bone and is used to transmit the sound waves in form of vibrations to the incus.
 Anvil is also known to be incus which is an anvil in shape and is used to transfer the vibrations from incus to the stapes.
 Stapes is attached to the incus at one end and fenestra at other ends. It is hollow in between forming a small window type formation.
These three contribute to forming a total of six bones in the whole skeleton structure.

The correct answer is option (B) that is Middle ear.

Note: The skull has a total of 28 bones, the pectoral girdle has 4 bones and the pelvic girdle has 2 hip bones in total. Skeleton contributes to the basic framework of our body which gives us strength and helps us in a controlled movement.