Final answer:
The answer to the specific question about when a sight gauge is required on pesticide tanks cannot be determined without further context or reference to local regulations, as these requirements may vary by jurisdiction.
Step-by-step explanation:
The question pertains to pesticide tanks and the capacity at which a sight gauge becomes a requirement. A sight gauge is an instrument used to show the level of liquid within a tank. This question is likely part of a larger discussion on safety measures and regulations when dealing with chemicals such as pesticides, which could be tied to an agriculture or chemistry curriculum. However, without further context or reference to specific regulations that determine the size threshold for requiring a sight gauge on pesticide tanks, it's not possible to accurately answer whether it is 20, 40, 50, or 100 gallons. In practice, the requirement for a sight gauge could vary by jurisdiction, and it's essential to refer to local guidelines and regulations. Nevertheless, it's critical to have such gauges to ensure proper monitoring and to prevent running out of material during application, which could jeopardize the effectiveness of pesticide application.