Is salt water a conductor or insulator ? Explain your answer

Salt itself is an insulator of electricity.

The conductivity of any solution depends on the movement of ions.

Ions are the charged species of the atom.

In salt the movement of these ions are not possible.

https://expandusceramics.com/qa/is-salt-a-conductor-or-insulator.html

Salt water is a insulator

Ohm's law tells you that i = v/r where v is equivalent voltage and r is equivalent resistance of the circuit
since all circuits have the same voltage, your question is really asking which circuit has the lowest total resistance, since the lower the resistance, the higher the current
circuit a has a resistance of 5 ohms; circuit c is in series so has a resistance of 10 ohms; circuit b is in parallel and therefore has a resistance of 2.5 ohms (review your notes on adding resistances in parallel and series); therefore b has the highest current