Final answer:
To remove ice from the sight glass safely and efficiently, a hair dryer should be used to gently melt the ice without causing damage.
Step-by-step explanation:
To remove ice from the sight glass, you should use a method that safely and effectively heats the ice without damaging the sight glass. Among the choices given, the best option is using a hair dryer. This method allows you to direct warm air onto the ice, causing it to melt. The choice of using hot water may be tempting, but it can cause a sudden temperature change, which might damage the glass or introduce additional water to the system. An ice pick could scratch or break the glass and is not recommended. Chemical sprays could be either ineffective or could introduce unwanted chemicals into the system.
By using a hair dryer, you ensure a controlled and gradual increase in temperature, which aligns with the principle of thermal expansion. This is similar to the concept of running hot water over a tight metal lid to loosen it, which works because of the expansion of the lid. A controlled and gentle heating is key to preventing any potential damage.