What is the symbol for inches of mercury?

Answer: C — HG

The symbol for inches of mercury is HG. This symbol is derived from the Latin word "Hydrargyrum," which means liquid silver, referring to mercury's appearance. In scientific contexts, particularly in meteorology and barometry, "inches of mercury" is a common way to measure atmospheric pressure. It indicates how high a column of mercury will rise under specific atmospheric conditions. The other options do not represent inches of mercury. The option representing IM does not correspond to any recognized unit in this context. IN is often used for inches more broadly, but it does not specifically denote inches of mercury. Lastly, M typically stands for meter, which is a unit of length, not pressure. Thus, HG is the correct and recognized symbol for inches of mercury.