- San Marino (Wikipedia)
San Marino (/ˌsæn məˈriːnoʊ/ SAN mə-REE-noh, Italian: [sam maˈriːno]; Romagnol: San Maréin or San Maroin), officially the Republic of San Marino (Italian: Repubblica di San Marino) and also known as the Most Serene Republic of San Marino (Italian: Serenissima Repubblica di San Marino), is a European microstate surrounded by Italy. Located on the northeastern side of the Apennine Mountains, it is the fifth-smallest country in the world, with a land area of just over 61 km2 (23+1⁄2 sq mi) and a population of 33,660 as of 2022.
- Rubidium (Wikipedia)
Rubidium is a chemical element; it has symbol Rb and atomic number 37. It is a very soft, whitish-grey solid in the alkali metal group, similar to potassium and caesium. Rubidium is the first alkali metal in the group to have a density higher than water. On Earth, natural rubidium comprises two isotopes: 72% is a stable isotope 85Rb, and 28% is slightly radioactive 87Rb, with a half-life of 48.8 billion years – more than three times as long as the estimated age of the universe.
