(i) The circuit arrangment for charging the cells is shows in figure
(ii) Effective emf of the circuit = `epsilon' - n epsilon`
Total resistance `= R+ nr`
Charging current `I= ("effective emf")/("total resistnance") = (epsilon' - n epsilon)/( R +nr)`
(iii) Pot. diff. across each charging cell `= epsilon + Ir`
`epsilon + ((epsilon' -n epsilon)/(R + nr)) r = (epsilon R + epsilon' r)/(R + nr)`
Pot. diff. across the series combination of n cells
`V = n (epsilon + Ir) = n ((epsilon R + epsilon'r)/(R + nr))`