What are the rules for writing the symbol of an element?

IUPAC —> International Union of Pure and Applied Chemistry approves the name of elements.

Symbols are the first one or two letters of the element’s name in English. The first letter of a symbol is always written as a capital letter (upper case) and the second letter as a small letter (lower case).

e.g., Hydrogen —> H

Some symbols are taken from the names of elements in Latin, German or Greek.

e.g., Symbol of iron is Fe, its Latin name is Ferrum.