Correct option (b)
Explanation:
Kirchhoff's law has to be applied to the whole loop.
If through one section (here the first battery) has zero potential difference, current cannot flow The question could have been modified. The statement that when the circuit is closed. the potential difference across the first cell is zero implies that in a series circuit, one part cannot conduct current which is wrong. Kirchhoff's law is violated. Assuming that ir1 = E as given in the question paper
some students could have found that R = r1 - r2 They have to be given marks.