Entries starting with R
- Radiocarbon datingRadiocarbon dating estimates the age of once-living material by measuring how much of its radioactive carbon-14 has decayed.
- Randomized controlled trialA randomized controlled trial tests a treatment by assigning participants to groups purely by chance, then comparing what happens to each group.
- Rare earth elementsRare earth elements are 17 metals, the 15 lanthanides plus scandium and yttrium, used in magnets, catalysts, screens and alloys.
- Replication crisisThe replication crisis is the finding that many published scientific results do not hold up when other researchers repeat the study with new data.
- Republic of the Congo: Geography, History and Key FactsThe Republic of the Congo (Congo-Brazzaville) is a west-central African nation on the Congo River, with Brazzaville as its capital and an oil-driven economy.
- Retrieval practiceRetrieval practice is deliberately recalling material from memory, which produces longer-lasting learning than rereading it.
- Riyadh: Geography, History, Culture and Key FactsRiyadh is the capital and most populous city of Saudi Arabia, on the Najd plateau, known for the Kingdom Centre tower.
- Romania: Geography, History, Culture and Key FactsRomania is a southeastern European country known for the Carpathian Mountains, the Danube Delta, and its global association with the Dracula legend.
- Rome: History, Geography, Culture and Key FactsRome is Italy's capital, built on two millennia of continuous history, famed for the Colosseum and as the historic center of Western Christianity.
- Russia: Geography, History, Culture and Key FactsRussia is the largest country in the world by land area, spanning Eastern Europe and northern Asia, known for Red Square and its cultural and space-exploration legacy.
- Rwanda: Geography, History, Culture and Key FactsRwanda is a densely populated, hilly central African country known for its mountain gorillas, rapid economic growth, and post-genocide recovery.