In saloons, there is always a characteristics smell due to the ammonia-based chemicals used in hair dyes and other products. Assume the initial concentration of ammonia molecules to be $1000 \,molecules/ m ^3$. Due to air ventilation, the number of molecules leaving in one minute is one tenth of the molecules present at the start of that minute. How long will it take for the concentration of ammonia molecules to reach $1 \,molecule / m ^3$ ?

  • [KVPY 2021]
  • A

    $7$ minutes

  • B

    $70$ minutes

  • C

    $100$ minutes

  • D

    Very long time which cannot be calculated.

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