State whether the following statement is true or false:
The chemical formulae of cupric oxide and cuprous oxide are $CuO$ and $Cu_{2}O$ respectively.

Write the chemical names of the following compounds:
$(a)$ $K_{2}SO_{4}$
$(b)$ $Mg_{3}(PO_{4})_{2}$
$(c)$ $NH_{4}Cl$
$(d)$ $ZnS$
$(e)$ $Na_{3}N$
$(f)$ $AgBr$

As per the law of definite proportion,carbon and oxygen combine in the ratio of $3:8$. Compute the mass of oxygen gas that would be required to react completely with $15\,g$ of carbon.

Which of the following represents $1 \, u$?

Which of the following symbols of elements are incorrect? Give their correct symbols:
$(a)$ Cobalt $CO$
$(b)$ Carbon $c$
$(c)$ Aluminium $AL$
$(d)$ Helium $He$
$(e)$ Sodium $So$

$(a)$ 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 $= Cl^{-}$)