Magnetite can be reduced with $CO$ to yield iron metal and carbon dioxide. Calculate the mass of magnetite (in $kg$) needed to obtain $4 \ kg$ of iron if the process is $80 \%$ efficient. [Atomic weight of $Fe$ and $O$ are $56 \ g$ and $16 \ g$,respectively]

$A$ metal exists as an oxide with formula $M_{0.96} O$. Metal $M$ can exist as $M^{2+}$ and $M^{3+}$ in its oxide $M_{0.96} O$. The percentage of $M^{3+}$ in the oxide is nearly: (in $\%$)

In the laboratory,chlorine is prepared by the reaction of manganese dioxide $(MnO_2)$ with aqueous hydrochloric acid $(HCl)$ as follows:
$4HCl_{(aq)} + MnO_{2(s)} \to 2H_2O_{(l)} + MnCl_{2(aq)} + Cl_{2(g)}$
How many grams of $HCl$ will react with $5.0 \ g$ of manganese dioxide (in $g$)?

How many moles of $H_2O$ are liberated when one mole of hydrated $MgCl_2$ is heated?

The heat of combustion of ethene $(C_2H_4)$ is $1411 \, kJ$. If a certain amount of ethene is burned to produce $6226 \, kJ$ of heat,what is the volume of $O_2$ (at $S.T.P.$) consumed in the process?

Volume of water needed to mix with $10 \ mL$ of $10 \ N \ HNO_3$ to get $0.1 \ N \ HNO_3$ is ............ $mL$.