How many significant figures are present in the following?

$126,000$

How many significant figures are present in the following?

$500.0$

How many significant figures are present in the following?

$2,0034$.

Round up the following up to three significant figures:

$34.216$.

Round up the following up to three significant figures:

$10.4107$.

Round up the following up to three significant figures:

$0.04597$.

Round up the following up to three significant figures:

$2808$.

Calculate the molarity of a solution of ethanol in water in which the mole fraction of ethanol is $0.040$ (Assume the density of water to be one). Use the data given in the following table to calculate the molar mass of naturally occurring argon isotopes:
Isotope               Isotopic molar mass                    Abundance

${}^{36}\mathrm{Ar}$                  $35.96755 \mathrm{g} {\mathrm{mol}}^{-1}$                 $0.337\%$

${}^{38}\mathrm{Ar}$                  $37.96272 \mathrm{g} {\mathrm{mol}}^{-1}$                 $0.063\%$

${}^{40}\mathrm{Ar}$                  $39.9624 \mathrm{g} {\mathrm{mol}}^{-1}$                  $99.600\%$.