Phosphorus has an electronic configuration in the simple form 2,8,5 and a spdf configuration of 1s² 2s² 2p⁶ 3s² 3p³.
The valence electrons in phosphorus (the electrons available for bonding) are 5. As a result, an atom of phosphorus shares its electrons with another atom to form COVALENT bonds. This is ideal since it would take a high amount of energy to release these five electrons, and it would be unlikely for atoms to lose 5 electrons to donate to phosphorus.
The evolution of sexual reproduction is a great puzzle in modern evolutionary biology. Many groups of eukaryotic organisms, especially most animals and plants, reproduce sexually. The evolution of sex between two organisms of the same species contains two related but different themes: its origin and its maintenance. However, since hypotheses for the origin of sex are difficult to test experimentally, most of the current work has focused on the maintenance of sexual reproduction. Biologists, including W. D. Hamilton, Alexei Kondrashov, and George C. Williams, have proposed various explanations for how sexual reproduction is maintained in a large set of different living things.
D) The Earth was hit by a one or more objects from space 65 million years ago. The iridium layer shows an extraterrestrial cause for the extinction at the Cretaceous Tertiary boundary, discovered by the Alvarez family. The first discovery of this layer was in the Bavarian alps, in Lattengebirge. The Alverez family proposed that the extinction of the dinosaurs was due to a large meteor hitting the Earth at the end of the Cretaceous period, marking the KT boundary with this clay layer which has a high content of iridium. Iridium is not common on Earth, but is common in meteors.
Limestone.
It is a sedimentary rock composed of calcite and aragonite. It is used as a building material mainly because it is easily available and easy to work with.
Limestone is used in the manufacture of steel as it is the primary raw material that helps to remove impurities from the iron ore and produces waste matter that has low melting point and viscosity
