Question

Write the complete symbol for the atoms with given atomic and mass no, $Z=18A=40$ and $A=9$
($Z=$Atomic no and $A=$mass)

Answer 1

A normal Argon atom has 18 electrons, 18 protons, and 22 neutrons. A normal atom is an atom that has a neutral charge. Since electrons are negative, protons are positive, and neutrons are neutral, that means the amount of electrons and protons is the same in a normal atom, in which case it is. In an ion, the atom will have either less or more electrons than protons, making it either positively or negatively charged.
Argon has 8 valence electrons (that means 8 of its electrons are orbiting the nucleus at the outermost orbital) making it a noble gas (the noble gases are on the rightmost part of the periodic table; Argon is the third from above).