Which element is a liquid nonmetal at room temperature?

Bromine, and it is one of only two elements that are liquid at ordinary room temperature - the other being mercury, a metal. Bromine is a dense, dark red-brown liquid that gives off a choking orange vapour at room temperature, and its name comes from the Greek for stench.

It is nasty to handle and was enormously useful. Silver bromide was the light-sensitive compound behind photographic film for a century; brominated compounds were the standard flame retardants in furniture, electronics and children's pyjamas; and ethylene dibromide was added to leaded petrol to scavenge the lead. Most of those uses have been curtailed - several brominated flame retardants persist in the environment and accumulate in bodies, and methyl bromide was phased out under the Montreal Protocol for damaging the ozone layer.

Most of it comes from very salty water. Bromine is extracted from the Dead Sea and from deep brine wells in Arkansas, which between them supply a large share of the world's production - so a global industrial chemical comes out of a handful of unusually briny holes in the ground.