Question

How many atoms are in 15.3 cm3 of mercury (at room temperature)?

Answer 1

Density = mass/volume

you know the volume 15.3 cm^3 which equals 15.3 mL
find the density of mercury (on a chart) then find the mass

once you have the mass use n=m/MW (moles equals mass over molecular weight)

find the number of moles (n) and multiply that by avogadros number to find the amount of particles (in your case, atoms) present.

Answer 2

ps. make sure you have matching units