What are $x$ and $y$ in the following reaction?
$x Pb_3O_4 \rightarrow y PbO + O_2$

Aluminium reacts with sulfuric acid to form aluminium sulfate and hydrogen. What is the volume of hydrogen gas in liters $(L)$ produced at $300 \ K$ and $1.0 \ atm$ pressure,when $5.4 \ g$ of aluminium and $50.0 \ mL$ of $5.0 \ M$ sulfuric acid are combined for the reaction?
(Use molar mass of aluminium as $27.0 \ g \ mol^{-1}, R = 0.082 \ atm \ L \ mol^{-1} \ K^{-1}$)

Assume carbon burns according to the following equation:
$2C_{(s)} + O_{2(g)} \rightarrow 2CO_{(g)}$
When $12 \ g$ of carbon is burnt in $48 \ g$ of oxygen,the volume of carbon monoxide produced is $...... \times 10^{-1} \ L$ at $STP$ [nearest integer].
[Given: Assume $CO$ as an ideal gas,molar mass of $C = 12 \ g \ mol^{-1}$,molar mass of $O = 16 \ g \ mol^{-1}$,and molar volume of an ideal gas at $STP$ = $22.7 \ L \ mol^{-1}$]

$A + 2B + 3C \rightleftharpoons AB_2C_3$. Reaction of $6.0 \ g$ of $A$,$6.0 \times 10^{23}$ atoms of $B$,and $0.036 \ mol$ of $C$ yields $4.8 \ g$ of compound $AB_2C_3$. If the atomic mass of $A$ and $C$ are $60$ and $80 \ amu$,respectively,the atomic mass of $B$ is .............. $amu$ (Avogadro no. $= 6 \times 10^{23}$)

Which of the following equations is written incorrectly?

$KMnO_4$ reacts with $KI$ in basic medium to form $I_2$ and $MnO_2$. When $250 \ mL$ of $0.1 \ M \ KI$ solution is mixed with $250 \ mL$ of $0.02 \ M \ KMnO_4$ in basic medium, what is the number of moles of $I_2$ formed?