Calculate the number of atoms in $60$ grams of carbon.

Write the chemical formulae for the following substances and calculate the molecular mass for each one of them:
$(a)$ Caustic potash
$(b)$ Baking soda
$(c)$ Limestone
$(d)$ Caustic soda
$(e)$ Ethanol
$(f)$ Common salt

State whether the following statement is true or false:
$A$ mole of any gas always occupies $22.4$ litres of volume at $0^{\circ} C$ and $1$ atmospheric pressure,which is known as standard temperature and pressure $(STP)$.

$(a)$ The ratio of hydrogen and oxygen in water is $1:8$ by mass. Find out their ratio by number of atoms in one molecule of water.
(Atomic mass: $H=1 \ u, O=16 \ u)$
$(b)$ Write the formulae of the following compounds:
$(i)$ Ammonium sulphate
$(ii)$ Magnesium chloride
(Given: Ammonium $= NH_{4}^{+}$,Sulphate $= SO_{4}^{2-}$,Magnesium $= Mg^{2+}$,Chloride $= Cl^{-}$)

Interpret the number of moles of oxygen atoms in $PO_{4}^{3-}$ ion.

The chemical formula of the oxide of an element $X$ is $X_2O_5$. Write the chemical formula of its chloride.