Which item is used to remove ice off the sight glass?

• A. Water
• B. Detergent
• C. Isopropyl alcohol
• D. Oil

Answer: (C)

The idea is to use a substance that melts ice quickly without leaving residue that could contaminate the system or obscure the sight glass. Isopropyl alcohol fits perfectly here because it has a very low freezing point and evaporates rapidly. A small amount applied to the sight glass will melt the ice and then dry away, leaving a clear view.

Water would just form more ice if the temperature is still near freezing, making the problem worse. Detergent could leave a soapy film or bubbles that obscure the view. Oil would leave a greasy residue and could contaminate the system or interfere with readings. So, the ice is removed best by isopropyl alcohol due to its rapid evaporation and lack of residue.