Carbon naturally occurs in two forms: diamond and graphite. why do these two forms have very different properties?

The differences in the properties of diamond and graphite is as a result of how their particles are arranged in space. This space arrangement leads to distinct crystal structures for the two compounds. In diamond, the carbon atoms are arranged in tetrahedral shape while in graphite the carbon atoms arrayed in planes.
 Hope this helps :)

Density is calculated using the following rule:
density = mass / volume
therefore:
mass = density * volume
mass of Hg = 13.6 * 60.2 = 818.72 grams

From the periodic table:
molar mass of Hg = 200.59 grams

number of moles = mass / molar mass
number of moles of Hg = 818.72 / 200.59 = 4.08 moles

each mole contains Avogadro's number of atoms.
Therefore,
number of atoms in the given sample = 4.08 * 6.022 * 10^23
                                                            = 2.456976 * 10^24 atoms