When a resistance of $2\, ohm$ is connected across the terminals of a cell, the current is $0.5\, A$. When the resistance is increased to $5\, ohm$, the current is $0.25\, A$. The $e.m.f.$ of the cell is ................. $V$
  • A$1$
  • B$1.5$
  • C$2$
  • D$2.5$
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