When we press the bulb of a dropper with its nozzle kept in water, air in the dropper is seen to escape in the form of bubbles. Once we release the pressure on the bulb, water gets filled in the dropper. The rise of water in the dropper is due to :

Options

A. pressure of water
B. gravity of the earth
C. shape of rubber bulb
D. atmospheric pressure

Explanation

To understand why water rises in the dropper when we release the pressure on the bulb, let's break down the explanation step by step.

### Step-by-Step Solution:

1. **Initial State**: When the dropper is submerged in water, it contains air in the upper part (the bulb) and is filled with water at the nozzle.

**Hint**: Consider what happens to the air inside the dropper when you press the bulb.

2. **Pressing the Bulb**: When we press the bulb of the dropper, we force the air inside the dropper out through the nozzle. This expulsion of air is visible as bubbles in the water.

**Hint**: Think about what happens to the volume of air when you apply pressure.

3. **Creating a Vacuum**: Once we release the pressure on the bulb, the air that was in the dropper has been expelled, creating a vacuum (an area with very low pressure) in the upper part of the dropper.

**Hint**: What happens to the air pressure when air is removed from a space?

4. **Role of Atmospheric Pressure**: The atmospheric pressure outside the dropper is now greater than the pressure inside the dropper (which is a vacuum). This difference in pressure causes the water from the outside to be pushed into the dropper to fill the vacuum.

**Hint**: Consider how pressure differences can cause movement of fluids.

5. **Water Filling the Dropper**: As the atmospheric pressure pushes down on the water in the container, it forces the water up into the dropper to fill the space left by the expelled air.

**Hint**: What force is acting on the water to make it rise into the dropper?

6. **Final State**: The water continues to rise in the dropper until the pressure inside the dropper equals the atmospheric pressure outside, at which point the water column stabilizes.

**Hint**: Think about the balance of forces and pressures in this scenario.

### Conclusion:
The rise of water in the dropper after releasing the pressure on the bulb is primarily due to atmospheric pressure acting on the water outside the dropper, which pushes the water into the dropper to fill the vacuum created by the expelled air.