For making good quality mirrors, plates of float glass are used. These are obtained by floating molten glass over a liquid metal, which does not solidify before glass. The metal used can be:

Mercury

The correct answer is option 1. Mercury.

Plates of float glass are obtained by floating molten glass over a mercury metal which does not solidify before glass. This is because mercury has the lowest melting point than all the given metals. That means mercury has the lowest freezing point. Mercury is the only element which remains in the liquid state at room temperature. So while the glass alloy is floated over mercury, the glass solidifies first as mercury has a freezing temperature of \(−38.83^∘C\) much lower than the glass.