Mass of mercury (Hg) in grams = density ( g `cm^(-3)) xx` volume `(cm^(3))`
`= 13.6 g cm^(-3) xx 1000 cm^(3) = 13600 g .`
`therefore` number of moles of mercury = `("mass of mercury in grams ")/("gram-atomic mass of mercury") = (13600 g)/(200 g) = 68.`