A wire of length $5\,m$ and radius $1\,mm$ has a resistance of $1\, ohm$. What length of the wire of the same material at the same temperature and of radius $2\,mm$ will also have a resistance of $1\, ohm$  .............. $m$
  • A$1.25$
  • B$2.5$
  • C$10$
  • D$20$
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