Calculate the molecular masses of $H_2$,$O_2$ and $Cl_2$.

What is the mass of:
$(a)$ $1$ mole of nitrogen atoms?
$(b)$ $4$ moles of aluminium atoms (Atomic mass of aluminium $= 27$)?
$(c)$ $10$ moles of sodium sulphite $(Na_2SO_3)$?

Write the chemical formulae of the following:
$(i)$ Magnesium chloride
$(ii)$ Calcium oxide
$(iii)$ Copper nitrate
$(iv)$ Aluminium chloride
$(v)$ Calcium carbonate.

Write down the chemical formulae of:
$(i)$ Sodium oxide
$(ii)$ Aluminium chloride
$(iii)$ Sodium sulphide
$(iv)$ Magnesium hydroxide

Calculate the formula unit masses of $ZnO, Na_2O, K_2CO_3$ given atomic masses of $Zn=65\,u, Na=23\,u, K=39\,u, C=12\,u$ and $O=16\,u$.

Define the atomic mass unit.