The given graph shows the variation of terminal potential difference V, across the combination of three identical cells in series to an external resistor versus the current i in the circuit. The internal resistance of each cell is:

1 Ω

The correct answer is Option (2) → 1 Ω

At $i = 0$: $V = E = 6 \; \text{V}$

At $V = 0$: $i = 2 \; \text{A}$

$i = \frac{E}{r_{eq}} \;\;\; \Rightarrow \;\; r_{eq} = \frac{E}{i} = \frac{6}{2} = 3 \; \Omega$

$r_{eq} = 3r \;\;\; \Rightarrow \;\;\; r = \frac{3}{3} = 1 \; \Omega$

Answer: $1 \; \Omega$