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Why is mercury useful in sealed electrical switches and relays?

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A periodic table element box for mercury shows its symbol Hg, atomic number 80, atomic weight 200.592, electron configuration, and name. Icons indicate mercury is a transition metal, liquid at room temperature, has a rhombohedral crystal structure, and is weakly basic. — mercury Properties of mercury.

Mercury is exceptionally useful in sealed electrical switches and relays primarily due to its high electrical conductivity.12

As the only elemental metal that remains liquid at room temperature, mercury can be used to open and close an electric circuit by tilting a reservoir of the liquid metal. Because it is a liquid, it provides a reliable, fluid contact point that can be easily manipulated within a sealed environment, which helps protect the internal components from external contaminants.312