Which of these nations is one of the leading countries in the development of litmus paper?

Litmus is a water-soluble mixture of different dyes extracted from lichens. It is often adsorbed onto filter paper to produce one of the oldest forms of pH indicator, used to test materials for acidity.

Litmus was used for the first time in about 1300 by Spanish physician Arnaldus de Villa Nova. From the 16th century onwards, the blue dye was extracted from some lichens, especially in the Netherlands.

The ability of litmus paper to change color when exposed to an acid or base is a result of litmus paper being infused with lichens. In the plant world, lichens are unique in that they are actually two distinct organisms, a fungus and an alga, living as one. Botanists classify lichens as fungi because it is the fungi that are considered to be responsible for sexual reproduction. However, each lichen has its own distinct name. Approximately 15,000 different types of lichens have been identified. Lichens can be found growing on rocks, trees, and walls, in the soil and even underwater in virtually all types of climates. Lichens are commonly used as gauge for environmental quality because they are sensitive to various pollutants. Several varieties of lichen are used to produce litmus including "rocella tinctoria", native to the Mediterranean, and "lecanora tartarea", a common lichen in the Netherlands. In fact, the Netherlands is the largest producers of litmus paper products.