What is ncl5? what is pcl5? which of the two compounds does not exist and why?

The compound NCl5 is the compound that cannot exist since the atom of nitrogen can react only to at most 3 other atoms. The PCl5 can exist in nature as phosphorus may bound with this number of other atoms and is named, phosphorus pentochloride. 

The activity series is shown in the attached picture. if the element is below the other, then you can displace the other. following the activity series as a guide, the reactions are as follows: nickel and aluminum chloride3 ni + 2 alcl₃  → 3 nicl₂ + 2 albarium and copper bromideba + cubr  →  no reaction because cu is less oxidizable than bapotassium nitrate and aluminum3 kno₃ + al  → al(no₃)₃ + 3 ksodium phosphate and zincnaso₄ + zn  → znso₄ + na

Answer trigonal pyramidal;