Balance the following chemical equations:
$(i)$ $Cu_2S + O_2 \to Cu_2O + SO_2$
$(ii)$ $Ca_3(PO_4)_2 + H_2SO_4 \to Ca(H_2PO_4)_2 + CaSO_4$

$100 \ g$ of propane is completely reacted with $1000 \ g$ of oxygen. The mole fraction of carbon dioxide in the resulting mixture is $x \times 10^{-2}$. The value of $x$ is ..... .
(Nearest integer)
[Atomic weight : $H=1.008$ ; $C=12.00$ ; $O=16.00$ ]

Calculate the mass of $AgCl$ precipitated when $25 \ mL$ of $35 \%$ solution of $AgNO_3$ and $25 \ mL$ of $11.6 \%$ solution of $NaCl$ are mixed. (in $g$)

$8 \ L$ of $H_2$ and $6 \ L$ of $Cl_2$ react to the maximum extent. Find the final volume of the reaction mixture in $L$. Assume $P$ and $T$ remain constant throughout the process.

When $22.4 \ L$ of $H_{2(g)}$ is mixed with $11.2 \ L$ of $Cl_{2(g)}$,each at $S.T.P.$,the moles of $HCl_{(g)}$ formed is equal to

At $100\,^oC$,a $1.5\,L$ vessel contains $0.4\,g$ of $O_2$ and $0.06\,g$ of $H_2$. $(a)$ What is the total pressure in the vessel? $(b)$ If the mixture reacts to form water at $100\,^oC$,which gas will remain in the vessel? What will be their partial pressures (in $,atm$)? $(R = 0.0821\, L\,atm\,mol^{-1}\,K^{-1})$.