If the size of bacteria is $1$ micron, what will be the number of it in $1 m$ length?

$1 \mathrm{micron}={10}^{-6}m$

$\because {10}^{-6}m$ space is occupied by $1$ bacteria.

$\therefore 1 m$ space will be occupied by

      ${10}^6 \mathrm{bacteria}=1 \mathrm{million} \mathrm{bacteria}$