Which structure reduces friction between joints?

The cartilage is the structure that reduces friction between joints.

Explanation:

Cartilage is the tissue between the bone joints. They are composed of several membranes and cellular groups. One of them called synovial membrane which provides lubricant to the edges of tissue that are touched by the bones. Reducing the friction and absorbing it so the body can move without obstacles.

lower, it's not as dense as chocolate syrup.

choco syrup is more like a solid than a liquid and even turns solid if it gets slightly cold,

orange juice however is a 95% liquid and has a very low viscosity