Which of the following is a ball and socket joint?

Options

A. hip joint
B. elbow joint
C. atlanto-axial joint
D. knee joint

Answer

To determine which of the following is a ball and socket joint, we need to understand what a ball and socket joint is and then analyze the options provided.

### Step-by-Step Solution:

1. **Definition of Ball and Socket Joint**:
A ball and socket joint, also known as a spheroidal joint, is a type of joint where a rounded surface (the "ball") of one bone fits into a cup-like depression (the "socket") of another bone. This structure allows for a wide range of movement in multiple directions.

2. **Movement Capability**:
Ball and socket joints allow for greater movement compared to other types of joints. They enable rotation and movement in various planes, making them highly versatile.

3. **Analyzing the Options**:
- **Option A: Hip Joint**: The hip joint is indeed a ball and socket joint. The head of the femur (thigh bone) fits into the acetabulum (cup-like socket) of the pelvis, allowing for a wide range of motion.
- **Option B: Elbow Joint**: The elbow joint is a hinge joint, which allows for flexion and extension but not rotation.
- **Option C: Atlanta-Axial Joint**: This joint is primarily a pivot joint that allows for rotation of the head, not a ball and socket joint.
- **Option D: Knee Joint**: The knee joint is primarily a hinge joint, allowing for bending and straightening, but not the full range of motion characteristic of ball and socket joints.

4. **Conclusion**:
Based on the analysis, the only option that qualifies as a ball and socket joint is **Option A: Hip Joint**.

### Final Answer:
**The correct answer is Option A: Hip Joint.**