The visible universe is estimated to contain $10^{22}$ stars. How many moles of stars are present in the visible universe?

Compute the number of ions present in $5.85 \, g$ of sodium chloride.

Give the chemical formulae for the following compounds and compute the ratio by mass of the combining elements in each one of them:
$(a)$ Ammonia
$(b)$ Carbon monoxide
$(c)$ Hydrogen chloride
$(d)$ Aluminium fluoride
$(e)$ Magnesium sulphide

Write the molecular formulae of all the compounds that can be formed by the combination of the following ions: $Cu^{2+}, Na^{+}, Fe^{3+}, Cl^{-}, SO_{4}^{2-}, PO_{4}^{3-}$.

Which of the following postulates of Dalton's atomic theory is challenged by the next generation of scientists?

Write the names of the following compounds:
$(a)$ $NiS$
$(b)$ $Mg(NO_3)_2$
$(c)$ $Na_2SO_4$
$(d)$ $Al(NO_3)_3$
$(e)$ $K_3PO_4$
$(f)$ $Ca_3N_2$