Calculate the number of moles of oxygen required to react with $6.8 \, g$ of ammonia in the following reaction:
$NH_3 + O_2 \to NO + H_2O$

Combustion of $50 \ mL$ methane is carried out with $150 \ mL$ of air containing $21 \%$ oxygen by volume. What will be the total volume of the gaseous mixture after the reaction? (Assume water is in the gaseous state and air contains $79 \%$ nitrogen by volume).
$CH_{4(g)} + 2O_{2(g)} \to CO_{2(g)} + 2H_2O_{(g)}$

If $0.5 \ mol$ of $BaCl_2$ is mixed with $0.1 \ mol$ of $Na_3PO_4$,what is the maximum number of moles of $Ba_3(PO_4)_2$ formed?

$3O_2 + 2N_2 \to 2N_2O_3$
$9 \ mol$ of $O_2$ and $14 \ mol$ of $N_2$ are allowed to react. When $3 \ mol$ of $O_2$ remains unreacted,how many moles of $N_2O_3$ would have been produced?

$100 \ mL$ of $0.05 \ M$ $Cu^{2+}$ aqueous solution is added to $1 \ L$ of $0.1 \ M$ $KI$ solution. The number of moles of $I_2$ and $Cu_2I_2$ formed are respectively:

How many moles of $PbCl_2$ will be obtained from the reaction between $6.5 \ g$ of $PbO$ and $3.2 \ g$ of $HCl$?