(3) It must always be necessarily connected just before the galvanometer to prevent high current entering the galvanometer.
(1) The galvanometer circuit can have large current when the jockey is pressed near the extreme ends of the poteniomeer wire due to the large potential difference across the wire, far away from the null point. Since the galvanometer is highly sensitive, it might get damaged due to this high current. A high resistance will reduce this current and protect the galvanometer. Hence (1) is a correct statement.
(2) At the null point the deflection in the galvanometer is zero as the current is zero. So the value of this high resistance does not decide the position of the null point, it only decreases the deflection when jockey is pressured at other points. So (2) is also a correct statement.
(3) Since a resistor only obstruct the flow of charge, the position of the resistor can be anywhere in the series part of the circuit. That means, the high resistance can be before, or after, the galvanometer. In either case the current gets reduced. So (3) is an incorrect statement (i.e. (3) is the correct answer to the question).
(4) When we approach the null point, the current through the galvanometer approaches zero or the deflection becomes almost zero. Here if we short circuit the high resistance, the deflection becomes obviously more, but the current will not to so high as to damage the galvanometer. Instead the short circuit of the high resistance will enable us to find the null point accurately. So (4) is also a correct statement.
