Explain why the melting and boiling points of covalent compounds are usually lower than those of ionic

How many moles of magnesium is 3.01 x10^22 atoms of magnesium?

If i initially have a gas at a pressure of 12 atm, a volume of 23 liters, and a temperature of 200 k, and then i raise the pressure to 14 atm and increase the temperature to 300 k, what is the new volume of the gas?

In what environment would mineral formation caused by high pressures and high temperatures most likely occur?