Question

Ammonia is a covalent cpnd does not conduct electricity but its aq. solution ammoium hydoxide is a weak electrolyte.

Answer 1

Hey Friend,

Ammonia is a covalent compound..true!
Well, electrical conductivity through an electrolyte depends on the presence of ions! and since ammonia does not contain ions, it doesn't conduct electricity

But, Ammonia in aqueous solution forms ammonium hydroxide with water which dissociates into Ammonium and hydroxide ions... 
NH3 + H2O ---> NH4OH
NH4OH ---> NH4+   +   OH-

And since it dissociates into ions, it conducts electricity

Hope it helps!

Answer 2

NH3 is a polar covalent compound and has slight charges present on it .so when water is added to it ions are formed which conducts electricity