What are the various letters used by Bohr to represent electron shells in an atom ?

The English letter used to represent atomic mass number is

What is the first rule of Bohr and Bury for electron distribution in an atom?

What are the symbols used for the shells which accommodate the electrons in various atoms ?

What is the maximum number of electrons in the outermost shell of an atom ?

Write the distribution of electrons in an atom of element whose atomic number is 18. What is special about the outermost electron shell (or valence shell) of the atom of this element ?

Write the distribution of electrons in an atom of element whose atomic number is 18. What is special about the outermost electron shell (or valence shell) of the atom of this element ?