Final answer:
The correct answer is option 1. cathode-ray tube.
Step-by-step explanation:
The TV monitor's picture tube is a technology no longer prevalent in modern-day electronics due to advancements in flat-screen technology. However, the picture tube is historically referred to as a cathode-ray tube (CRT). In a CRT, a beam of electrons is directed towards a screen that has been coated with phosphor. When these electrons strike the phosphor coating, they produce the visible image on the screen.
This is different from the other tubes listed, such as the pick-up tube, vidicon tube, and closed-circuit tube, which have different functions in electronics and image processing.
Furthermore, when CRTs operate at high accelerating potentials, such as 30-kV, it's plausible for them to generate not only visible light but also X rays. This is due to the high-energy electrons interacting with the materials in the tube, which can result in X-ray production, a characteristic also observed in other devices that accelerate electrons, like X-ray machines.