The correct answer is (d) atmospheric pressure.
Explanation: When the bulb is pressed, it creates a lower pressure inside the dropper. Because the atmospheric pressure on the water outside the dropper is greater, the water is pushed into the dropper to fill the space created by the decreased pressure inside.
Why other options are incorrect:
(a) pressure of water:
The pressure of water doesn’t cause the water to rise in this scenario. It’s the difference in pressure between the inside of the dropper and the surrounding atmosphere that forces the water in.
(b) gravity of the earth:
While gravity does play a role in the movement of objects, it’s not the primary factor causing the water to rise. The force driving the water is the atmospheric pressure.
(c) shape of rubber bulb:
The shape of the bulb helps in applying pressure, but it’s not the direct cause of the water rising. It’s the pressure difference created by the bulb that matters.