3.
If I have 0.5 moles of Magnesium then how many atoms of magnesium is
present?

1 mole of MgO contains Avogadro's number of molecules which is 6.023×10^23

molecules.

0.5 mole of MgO will contain 0.5×6.023×10^23

=3.0115×10^23 molecules

each chemical family is represented as a group or column on the periodic table. based on chemical properties, there are 6 types of chemical families. group 1 represents alkali metals, group 2 represents alkaline earth metals, groups 3 to 12 represent transition metals, groups 13 to 16 represent non-metals and other metals, group 17 represents halogens and group 18 represents noble gases.