$$\eqalign{ & \mathop {AgN{O_3}}\limits_{x\,g} + \mathop {NaCl}\limits_{5.85\,g} \to \mathop {NaN{O_3}}\limits_{8.5\,g} + \mathop {AgCl}\limits_{14.35\,g} \cr & x + 5.85 = 8.5 + 14.35 \cr & \Rightarrow x = 17 \cr} $$

$$1\,mole\,\,{\text{occupies a volume of}}$$       $$22.4\,L\,\,at\,\,STP$$
$$\eqalign{ & {\text{Mass of }}1{\text{ }}mole{\text{ of a gas}} \cr & = {\text{Density}} \times {\text{Volume}} \cr & {\text{ = 1}}{\text{.78}} \times {\text{22}}{\text{.4}} \cr & {\text{ = 39}}{\text{.9}}\,{\text{g}} \cr} $$

\[\underset{\begin{smallmatrix} 2\,moles \\ 2\times 58.5=117\,g \end{smallmatrix}}{\mathop{2NaCl}}\,+Mn{{O}_{2}}+3{{H}_{2}}S{{O}_{4}}\to 2NaHS{{O}_{4}}+MnS{{O}_{4}}+\underset{\begin{smallmatrix} 1\,mole \\ 22.4\,L\left( STP \right) \end{smallmatrix}}{\mathop{C{{l}_{2}}}}\,+2{{H}_{2}}O\]
$$117\,g\,\,{\text{of}}\,\,NaCl \equiv 22.4\,L\,\,{\text{of}}\,\,C{l_2}$$
$$50\,g\,\,{\text{of}}\,\,NaCl \equiv \frac{{22.4}}{{117}} \times 50$$      $$ = 9.57\,L\,\,{\text{of}}\,\,C{l_2}\,\,{\text{at}}\,\,STP$$

\[\underset{28\,g}{\mathop{{{C}_{2}}{{H}_{4}}}}\,+\underset{\begin{smallmatrix} 3\times 32 \\ =96\,g \end{smallmatrix}}{\mathop{3{{O}_{2}}}}\,\to 2C{{O}_{2}}+2{{H}_{2}}O\]
$$28\,g\,\,{\text{of}}\,\,{C_2}{H_4}\,\,{\text{requires}}\,\,96\,g\,\,{\text{of}}\,\,{O_2}$$
$$560\,g\,\,{\text{of}}\,\,{C_2}{H_4}\,\,{\text{requires}}\,\frac{{96}}{{28}} \times 560$$       $$ = 1920\,g\,\,{\text{or}}\,\,1.92\,kg\,\,{\text{of}}\,\,{O_2}$$