Two identical cells send the same current in 2 Ω resistance, whether connected in series or in parallel. The internal resistance of the cell should be
1 Ω
2 Ω
12 Ω
2.5 Ω
In series, i1= 2E2+2r
In parallel, i2= E2+r2 = 2E4+r
Since i1= i2⇒ 2E4+r = 2E2+2r ⇒ r=2Ω