In the 1920s, who created the Left-Step Periodic Table (LSPT) of the chemical elements, basing the positions of the elements on patterns in the arrangement of electrons around the atomic nucleus?
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Correct answer: C
Explanation
The correct answer is option 3 i.e. Charles Janet.
In the 1920s, the Left-Step Periodic Table (LSPT) was created by Charles Janet, a French engineer and chemist. He based the arrangement of elements on the structure of atomic electron configurations, particularly the order in which electron orbitals are filled. Unlike the traditional periodic table, Janet's LSPT starts with the s-block on the right and emphasizes the role of quantum numbers and electron shells, offering a more logical and symmetrical layout based on atomic structure. His approach highlighted the periodicity arising from quantum mechanics and provided deeper insights into elemental properties, though it gained wider recognition only much later.