A. Bohr

A. Bohr refers to Niels Bohr, a Danish physicist who made significant contributions to our understanding of atomic structure and quantum mechanics in the early 20th century. He proposed the Bohr model of the atom, which suggests that electrons orbit the nucleus in specific energy levels. This model explained how atoms absorb and emit energy, leading to the development of quantum theory. Bohr's work earned him the Nobel Prize in Physics in 1922 and laid the foundation for much of modern physics, influencing areas such as nuclear energy and the development of quantum mechanics.