What mass in $g$ of hydrated oxalic acid $(H_2C_2O_4 \cdot 2H_2O)$ should be added for complete neutralization of $100 \ mL$ of $0.2 \ N \ NaOH$ solution?

$20 \, mL$ of $1 \, N \, KMnO_4$ solution reacts with $20 \, mL$ of oxalic acid solution. The weight of oxalic acid crystals $(H_2C_2O_4 \cdot 2H_2O)$ in the $1 \, N$ solution is . . . . . . $g$.

In an aqueous solution of $A_2B_3$,it undergoes complete ionization according to the reaction $A_2B_3 \rightleftharpoons 2A^{+3} + 3B^{-2}$. The concentration of $A^{+3}$ is equal to......

$A$ sample of $CaCO_3$ and $MgCO_3$ weighing $2.21 \ g$ is ignited to a constant weight of $1.152 \ g$. The composition of the mixture is:
(Given molar mass in $g \ mol^{-1}: CaCO_3 = 100, MgCO_3 = 84$)

$100 \ mL$ of $PH_3$ on decomposition produces phosphorus and hydrogen. The change in volume is ............... $mL$ increase.

In the Victor Meyer method,$0.2 \ g$ of a volatile substance displaces $56 \ mL$ of air at $STP$. The molar mass of the substance is: