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1 dzień temu · Oxygen is a chemical element; it has symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as well as with other compounds. Oxygen is the most abundant element in Earth's crust, and after hydrogen and helium, it ...
1 dzień temu · Africa is the world's second largest and second-most populous continent after Asia. At about 30.3 million km 2 (11.7 million square miles) including adjacent islands, it covers 20% of Earth 's land area and 6% of its total surface area. [7] With 1.4 billion people [1] [2] as of 2021, it accounts for about 18% of the world's human population.
