Who discovered three chemical elements: cerium, thorium and selenium, and devised the modern method by which one or two letters are used to symbolise elements?

Jacob Berzelius

The correct answer is option 3. Jacob Berzelius.

Jacob Berzelius, a Swedish chemist, made significant contributions to the field of chemistry during the 19th century. He is credited with the discovery of several chemical elements, including cerium (Ce), thorium (Th), and selenium (Se). Berzelius was instrumental in advancing the understanding of the composition of compounds and the development of modern chemical notation.

One of his key contributions was the introduction of a systematic and concise method of representing elements using symbols. Before Berzelius, there was no standardized system for representing elements, and different scientists used various symbols, often based on the element's name in Latin or another language.

Berzelius proposed the use of one or two letters to symbolize elements, and he introduced a system of using the first letter (or the first and second letters) of an element's Latin name. For example:

Ce for cerium

Th for thorium

Se for selenium

This notational system provided a more convenient and uniform way of representing elements and compounds. It laid the groundwork for the development of the modern chemical notation and symbol system that we use today. Berzelius's contributions were essential in organizing the growing body of chemical knowledge and making it more accessible and understandable for scientists worldwide.