Answer:
In chemical bonding: Arrangement of the elements. The horizontal rows of the periodic table are called periods. Each period corresponds to the successive occupation of the orbitals in a valence shell of the atom, with the long periods corresponding to the occupation of the orbitals of a d subshell.
Explanation:
 
        
                    
             
        
        
        
The correct option is C.
A Lewis dot diagram is a representation of the valence electron of  an atom, which uses dot around the symbol of the atom. Chlorine has seven electrons in its outermost shell, these seven electrons are arranged in form of dot around the atom of chlorine. If you count the number of dot given in option C, you will notice that they are seven.
        
                    
             
        
        
        
Answer:
3)Some gas molecules move further apart and some move closer together.
Explanation:
because When more gas particles enter a container, there is less space for the particles to spread out, and they become compressed. The particles exert more force on the interior volume of the container. This force is called pressure. There are several units used to express pressure.
 
        
             
        
        
        
Lead.  
Lead paint was a big problem and now lead has been removed from paint because it was found to be dangerous to the health of living organisms.
Hope this helps! :)