If $K$ and $L$ shells of an atom are full,then what would be the total number of electrons in the atom?

An atom with $3$ protons and $4$ neutrons will have a valency of

Summarize the rules for writing the distribution of electrons in various shells for the first eighteen elements.

$(a)$ Which of the following electronic configurations are not possible? Give reasons.
$(i)$ $X: 2, 8, 4$
$(ii)$ $Y: 3, 8, 2$
$(iii)$ $Z: 2, 8, 9$
$(b)$ Write electronic configurations of the following elements and predict their valencies:
Fluorine: $9$,Aluminium: $13$,Argon: $18$

Find the valency of chlorine,sulphur,and magnesium.

Write down the electron distribution of chlorine atom. How many electrons are there in the $L$ shell? (Atomic number of chlorine is $17$).