A dropper to fill ink works because of which of the following ?

Options

A. Friction
B. Magnetic force
C. Air pressure
D. Electrostatic force

Explanation

To determine how a dropper works to fill ink, let's analyze the options provided and understand the mechanism involved step by step.

### Step-by-Step Solution:

1. **Understanding the Dropper Mechanism**:
- A dropper consists of a rubber bulb at the top and a narrow tube at the bottom. When the rubber bulb is squeezed, the volume inside the bulb decreases.

**Hint**: Think about what happens to the air inside the dropper when you squeeze it.

2. **Squeezing the Bulb**:
- When you press the rubber bulb, the air inside is forced out through the narrow tube. This action creates a low-pressure area inside the dropper.

**Hint**: Consider what happens to the air pressure inside the dropper when the bulb is squeezed.

3. **Ink Filling**:
- As the air is expelled, the pressure inside the dropper decreases. The atmospheric air pressure outside the dropper is now greater than the pressure inside the dropper. This difference in pressure causes the ink from the ink pot to be pushed up into the dropper.

**Hint**: Relate the concept of pressure difference to how liquids move in response to changes in pressure.

4. **Transferring Ink**:
- When you want to transfer the ink, you can again squeeze the bulb to create a high-pressure situation, forcing the ink out of the dropper and into another container, like an ink pen.

**Hint**: Think about how the pressure changes when you release the bulb after filling it with ink.

5. **Conclusion**:
- The dropper works primarily because of **air pressure**. The mechanism relies on creating a pressure difference that allows the ink to be drawn into the dropper and then expelled when needed.

### Final Answer:
The dropper to fill ink works because of **air pressure**.