Two cells of emf $2\, E$ and $E$ with internal resistance $r _{1}$ and $r _{2}$ respectively are connected in series to an external resistor $R$ (see $figure$). The value of $R ,$ at which the potential difference across the terminals of the first cell becomes zero is
  • A$r _{1}+ r _{2}$
  • B$\frac{ r _{1}}{2}- r _{2}$
  • C$\frac{ r _{1}}{2}+ r _{2}$
  • D$r _{1}- r _{2}$
JEE MAIN 2021, Diffcult
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