Which element with the atomic number 31 will melt if held in the hand?

Gallium is a chemical element with the symbol Ga and atomic number 31. Elemental gallium is a soft, silvery metal at standard temperature and pressure; however, in its liquid state, it becomes silvery white. If too much force is applied, the gallium may fracture conchoidally. It is in group 13 of the periodic table and thus has similarities to the other metals of the group, aluminium, indium, and thallium.

Gallium does not occur as a free element in nature, but as gallium (III) compounds in trace amounts in zinc ores and in bauxite. Elemental gallium is a liquid at temperatures greater than 29.76 °C (85.57 °F), and will melt in a person's hands at a normal human body temperature of 37.0 °C (98.6 °F).

The melting point of gallium is used as a temperature reference point. Gallium alloys are used in thermometers as a non-toxic and environmentally friendly alternative to mercury and can withstand higher temperatures than mercury. An even lower melting point of −19 °C (−2 °F), well below the freezing point of water, is claimed for the alloy galinstan (62–⁠95% gallium, 5–⁠22% indium, and 0–⁠16% tin by weight), but that may be the freezing point with the effect of supercooling.

Since its discovery in 1875, gallium has been used to make alloys with low melting points. It is also used in semiconductors as a dopant in semiconductor substrates.