Number of cells of emf E each and internal resistance ‘r’ each are connected in series by reversing the polarity of them alternately. Then for the system

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Emf is zero and internal resistance is zero if N is even

Emf is NE and internal resistance is Nr if N is odd

Emf is zero and internal resistance is Nr if N is even

Emf is E and internal resistance is r if N is odd

answer is D.

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Detailed Solution

When N cells are joined in series equivalent emf =E+E+E+.........

and internal resistance r+r+r+........=nr

But if opposite polarities are joined internal resistance will be same as nr but emf will be

E-E+E-E.......

if n is odd it will be E if it is even it will be zero

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