Three copper wires of lengths and cross sectional areas are (l , A) (2l, A/2) and (l/2 , 2A). Resistance is minimum in

wire of cross sectional area A/2                                   wire of cross sectional area A  wire of cross sectional area 2A     same in all the three cases

wire of cross sectional area 2A

Diameter is reduced to half, length increases 4 times as mass of material remains the same. $ R = \rho \frac{l}{A} $ Resistance is minimum when length is minimum and area is maximum.