In an arrangement, 3n cells of emf ε and internal resistance r are connected in series. Out of 3n cells, the polarity of n cells is reversed. Current in the circuit is:

Explanation

In this arrangement, you have 3n cells, each with emf ε and internal resistance r, connected in series. When n cells have their polarity reversed, these cells effectively subtract their emf from the total emf of the circuit. So, the effective emf is (3n - n)ε = 2nε - nε = ε. The total internal resistance is the sum of the internal resistances of all 3n cells, which is 3n * r = 3r. Therefore, the current in the circuit is given by Ohm's Law as i = Eeffective / reffective = ε / 3r.Option C correctly reflects this calculation. Options A, B, and D incorrectly calculate the current by either ignoring the reversed cells or incorrectly combining the resistances and emfs.