Which of the following are strong electrolytes?
H2SO4
NaOH
As H2SO4 is strong acid it is dissociates completely in water, same with NaOH which is strong base, so both are strong electrolytes.
Urea dissociates partially in water so it is a weak electrolyte.
Whereas benzene doesn’t dissociate at all so it is a non-electrolyte.