The correct answer is option 1: Partial vacuum produced inside the glass tube.

A syringe is a hollow glass tube that has a lower end tapered to a nozzle. It is commonly used to draw in and dispense liquids. The mechanism by which a liquid can be drawn into a syringe is by creating a partial vacuum inside the glass tube.

In simpler terms, when the plunger of the syringe is pulled back, it creates a space with lower pressure inside the syringe. This decrease in pressure causes the liquid to be sucked into the syringe through the nozzle. This process is known as suction or aspiration.

The other options mentioned - diffusion, surface tension, and capillary action - are not directly related to the process of drawing liquid into a syringe. Diffusion refers to the movement of particles from an area of high concentration to low concentration. Surface tension is the force that causes the surface of a liquid to behave like a stretched elastic sheet. Capillary action is the ability of a liquid to flow in narrow spaces against the force of gravity. None of these processes are involved in the specific task of drawing liquid into a syringe.