How many significant digits are present in the following numbers? Convert each to scientific notation.

$($i$)10\mathrm{.}020($v$)$

$($ii$)0\mathrm{.}00034($vi$)999$

$($iii$)2500.($vii$)$ population $152,000$ grams

$($iv$)042\mathrm{.}02($viii$)0\mathrm{.}000001$ grams