The earth binds the atmosphere because of

Options

A. Gravity
B. Oxygen between earth and atrnosphere
C. Both (a) and (b)
D. None

Explanation

To solve the question "The earth binds the atmosphere because of," we need to analyze the options provided and understand the underlying physics concepts.

### Step-by-Step Solution:

1. **Understanding the Atmosphere**:
- The atmosphere is a layer of gases surrounding the Earth. It is composed of various gases, primarily nitrogen and oxygen, which have mass.

**Hint**: Remember that the atmosphere is not just a single gas but a mixture of gases.

2. **Role of Gravity**:
- The Earth has a gravitational force that pulls objects towards its center. This force is responsible for keeping the atmosphere bound to the Earth.

**Hint**: Consider how gravity affects all objects with mass, including gases in the atmosphere.

3. **Mass of Atmospheric Gases**:
- Since the gases in the atmosphere have mass, they are affected by the gravitational pull of the Earth. This means that the gases are attracted towards the Earth, which helps in maintaining the atmosphere.

**Hint**: Think about how the mass of an object influences the gravitational force it experiences.

4. **Evaluating Options**:
- **Option A: Gravity** - This is correct, as gravity is the force that binds the atmosphere to the Earth.
- **Option B: Oxygen between Earth and atmosphere** - This is incorrect because while oxygen is a component of the atmosphere, it does not bind the atmosphere to the Earth.
- **Option C: Both A and B** - This is incorrect because only gravity is responsible for binding the atmosphere.
- **Option D: None of these** - This is also incorrect as gravity is indeed the binding force.

5. **Conclusion**:
- The correct answer is **gravity**. It is the gravitational force exerted by the Earth that keeps the atmosphere from drifting away into space.

### Final Answer:
The Earth binds the atmosphere because of **gravity**.