Answer :
Covalent compound : It is defined as the compound which is formed by the sharing of electrons between the atoms forming a compound.
The covalent compound are usually formed when two non-metals react.
Ionic compound : It is defined as the compound which is formed when electron gets transferred from one atom to another atom.
All the polyatomic ions always form an ionic compound.
Polyatomic ions : It is a charged species that composed of two or more atoms and these charged species are bonded by the covalent bond.
For the given options:
Option A: 
This compound is formed by the combination of potassium, 
which is a metal and 
ion which is a polyatomic ion. Thus, it will form an ionic compound.
Option B: 
This compound is formed by the combination of magnesium, 
which is a metal and 
ion which is a polyatomic ion. Thus, it will form an ionic compound.
Option C: 
Hydrogen and sulfur, both are non-metals and they will form a covalent compound.
Option D: 
This compound is formed by the combination of silver, 
which is a metal and sulfur, 
which is a non-metal. Thus, it will form an ionic compound.
Option E: 
Nitrogen and chlorine, both are non-metals and they will form a covalent compound.
Option F: 
This compound is formed by the combination of cobalt, 
which is a metal and 
ion which is a polyatomic ion. Thus, it will form an ionic compound.
