Molarity of a given orthophosphoric acid solution is $3 \ M$. Its normality is (in $N$)

$12 \ g$ of $Mg$ (atomic mass $24$) on reacting completely with acid gives hydrogen gas,the volume of which at $STP$ would be ............... $L$.

$20 \ mL$ of methane is completely burnt using $50 \ mL$ of oxygen. The volume of the gas left after cooling to room temperature is (in $mL$)

$A$ $100 \ mL$ solution was made by adding $1.43 \ g$ of $Na_2CO_3 \cdot xH_2O$. The normality of the solution is $0.1 \ N$. The value of $x$ is .......... (The atomic mass of $Na$ is $23 \ g/mol$):

$150 \ g$ $CaCO_3$ sample was taken. On its complete decomposition $56 \ g$ $CaO$ is produced. The $\%$ purity of the sample is .............. $\%$

In dilute aqueous $H_2SO_4$,the complex diaquodioxalatoferrate$(II)$ is oxidized by $MnO_4^-$. For this reaction,the ratio of the rate of change of $[H^{+}]$ to the rate of change of $[MnO_4^-]$ is