When all the cells are connected correctly, then Equivalent emf = 4E and effective resistance = 4r
If one of the cell is connected wrongly then, effective internal resistance will remain unchanged while, equivalent emf is E′=E(n−2m) where n is total number of cells; m is number of wrongly connected cells. Therefore,
E′=E(4−2×1)=E(4−2)=2E
⇒ equivalent emf = 2E and effective internal resistance = 4r