This is the simplest type of joint, found in your elbows, knees, fingers, and toes. it allows movement in only one direction. it is a joint

Hinge Joints

Explanation:

A hinge joint can be defined as the class of synovial joints that  includes fingers, toes, ankles, elbows.

This joint is formed between two or more bones where the bones can only move along single axis.

It does not moves in both the directions. It provides strength to the different parts of the body through this joint. A hinge joint, also known as a ginglymus joint.

oxygen +1 most likely

sodium i think the chemical element of atomic number 11, a soft silver-white reactive metal of the alkali metal group.