Merge pull request #4609 from oxygen-dioxide/chemistry

Add chemistry topic

topics/chemistry/index.md

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+---
+display_name: Chemistry
+short_description: Chemistry is the scientific study of substances, their structure, properties, and reactions.
+topic: chemistry 
+wikipedia_url: https://en.wikipedia.org/wiki/Chemistry
+---
+Chemistry is a branch of natural science that studies substances, their structure, properties, and reactions when they combine or separate. It plays a crucial role in understanding the composition of matter and its transformations. Chemistry can be divided into several sub-disciplines including organic chemistry, inorganic chemistry, physical chemistry, analytical chemistry, and biochemistry. These areas explore everything from the synthesis of new molecules to the chemical processes happening within living organisms.