In electron dot structure,the valence shell electrons are represented by crosses or dots.
$(a)$ The atomic number of chlorine is $17$. Write its electronic configuration.
$(b)$ Draw the electron dot structure of chlorine molecule $(Cl_2)$.

(N/A) The atomic number of chlorine is $17$. Its electronic configuration is $2, 8, 7$ in $K, L, M$ shells respectively.
$(b)$ Each chlorine atom has $7$ valence electrons. To complete its octet,each chlorine atom shares one electron with another chlorine atom,forming a single covalent bond. The electron dot structure is as follows:
:Cl:Cl: (with $6$ dots around each Cl and $2$ shared dots in the middle)