(i) The connections are made of thick copper wires to minimise the resistance of connecting wire Because the connection resistance have not been accounted in the formula.
Resistance is inversely proportional to cross sectional area so thick wire has low resistance
(ii) The error in the measured value of unknown resistance S using bridge wire will be minimum, when the null point is obtained at the middle of bridge wire. In this situation, the end error of the bridge will be ineffective.